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This document describes yabasic. You will find information about the yabasic interpreter (the program yabasic under Unix or yabasic.exe under Windows) as well as the language itself.
This document applies to version 2.750 of yabasic
However, this document does not contain the latest news about yabasic or a FAQ. As such information tends to change rapidly, it is presented online only at www.yabasic.de.
Although basic has its reputation as a language for beginning programmers, this is not an introduction to programming at large. Rather this text assumes, that the reader has some (moderate) experience with writing and starting computer programs.
yabasic is a traditional basic interpreter. It understands most of the typical basic-constructs, like goto, gosub, line numbers, read, data or string-variables with a trailing '$'. But on the other hand, yabasic implements some more advanced programming-constructs like subroutines or libraries (but not objects). yabasic works much the same under Unix and Windows.
yabasic puts emphasis on giving results quickly and easily; therefore simple commands are provided to open a graphic window, print the graphics or control the console screen and get keyboard or mouse information. The example below opens a window, draws a circle and prints the graphic:
open window 100,100 open printer circle 50,50,40 text 10,50,"Press any key to get a printout" clear screen inkey$ close printer close window
This example has fewer lines, than it would have in many other programming languages. In the end however yabasic lacks behind more advanced and modern programming languages like C++ or Java. But as far as it goes it tends to give you results more quickly and easily.
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Once, yabasic has been set up correctly, there are three ways to start it:
Rightclick on your desktop: The desktop menu appears with a submenu named new. From this submenu choose yabasic. This will create a new icon on your desktop. If you rightclick on this icon, its context menu will appear; choose Execute to execute the program.
As a variant of the way described above, you may simply create a file with the ending .yab (e.g. with your favorite editor). Everything else then works as described above.
From the start-menu: Choose yabasic from your start-menu. A console-window will open and you will be asked to type in your program. Once you are finished, you need to type return twice, and yabasic will parse and execute your program.
This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a save-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs.
Under Windows yabasic will mostly be invoked by double-clicking on an appropriate icon; this way you do not have a chance to specify any of the commandline options below. However, advanced users may add some of those options to the appropriate entries in the registry.
All the options below may be abbreviated, as long as the abbreviation does not become ambigous. For example, you may write -e instead of -execute.
Prints a short help message, which itself describes two further help-options.
Prints the version of yabasic.
Sets the position of the graphic window, that is opened by open window (the size of this window, of course, is specified within the open window-command). An example would be -geometry +20+10, which would place the graphic window 10 pixels below the upper border and 20 pixels right of the left border of the screen. This value cannot be changed, once yabasic has been started.
Name of the font, which will be used for graphic-text; can be any of decorative, dontcare, modern, roman, script, swiss. You may append a fontsize (measured in pixels) to any of those fontnames; for example -font swiss30 chooses a swiss-type font with a size of 30 pixels.
Create a standalone program (whose name is specified by NAME-OF-STANDALONE-PROGRAM) from the yabasic-program, that is specified on the commandline. See the section about creating a standalone-program for details.
With this option you may specify some yabasic-code to be executed rigth away.This is useful for very short programs, which you do not want to save within a file. If this option is given, yabasic will not read any code from a file. Let's say, you have forgotten some of the square numbers between 1 and 10; in this case the command yabasic -e 'for a=1 to 10:print a*a:next a' will give you the answer immediately.
Change the infolevel of yabasic, where INFOLEVEL can be one of debug, note, warning, error and fatal (the default is warning). This option changes the amount of debugging-information yabasic produces. However, normally only the author of yabasic (me !) would want to change this.
Print the embedded documentation of the named program. The embedded documentation of a program consists of all the comments within the program, which start with the special keyword doc. This documentation can also be seen by choosing the corresponding entry from the context-menu of any yabasic-program.
Change the directory, wherein libraries will be searched and imported (with the import-command). See also this entry for more information about the way, libraries are searched.
Like every other icon under Windows, the icon of every yabasic-program has a context menu offering the most frequent operations, that may be applied to a yabasic-program.
This will invoke yabasic to execute your program. The same happens, if you doubleclick on the icon.
notepad will be invoked, allowing you to edit your program.
This will present the embedded documentation of your program. Embedded documentation is created with the special comment doc.
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If your system administrator (vulgo root) has installed yabasic correctly, there are three ways to start it:
You may use your favorite editor (emacs, vi ?) to put your program into a file (e.g. foo). Make sure that the very first line starts with the characters '#!' followed by the full pathname of yabasic (e.g. '#!/usr/local/bin/yabasic'). This she-bang-line ensures, that your Unix will invoke yabasic to execute your program (see also the entry for the hash-character). Moreover, you will need to change the permissions of your yabasic-program foo, e.g. chmod u+x foo. After that you may invoke yabasic to invoke your program by simply typing foo (without even mentioning yabasic). However, if your PATH-variable does not contain a single dot ('.') you will have to type the full pathname of your program: e.g. /home/ihm/foo (or at least ./foo).
Save your program into a file (e.g. foo) and type yabasic foo. This assumes, that the directory, where yabasic resides, is contained within your PATH-variable.
Finally your may simply type yabasic (maybe it will be necessary to include its full pathname). This will make yabasic come up and you will be asked to type in your program. Once you are finished, you need to type return twice, and yabasic will parse and execute your program.
This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a save-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs, i.e. for using yabasic as some sort of fancy desktop calculator.
yabasic accepts a number of options on the commandline. All these options below may be abbreviated, as long as the abbreviation does not become ambigous. For example you may write -e instead of -execute.
Prints a short help message, which itself describes two further help-options.
Prints the version of yabasic.
Define the foreground color for the graphics-window (that will be opened with open window). The usual X11 colornames, like red, green, … are accepted. This value cannot be changed, once yabasic has been started.
Define the background color for the graphics-window. The usual X11 colornames are accepted. This value cannot be changed, once yabasic has been started.
Sets the position of the graphic window, that is opened by open window (the size of this window, of course, is specified with the open window-command). An example would be +20+10, which would place the graphic window 10 pixels below the upper border and 20 pixels right of the left border of the screen. Note, that the size of the window may not be specified here (well it may, but it will be ignored anyway). This value cannot be changed, once yabasic has been started.
Specify the display, where the graphics window of yabasic should appear. Normally, however this value will be already present within the environment variable DISPLAY.
Name of the font, which will be used for text within the graphics window.
With this option you may specify some yabasic-code to be executed rigth away.This is useful for very short programs, which you do not want to save to a file. If this option is given, yabasic will not read any code from a file. E.g.
yabasic -e 'for a=1 to 10:print a*a:next a'prints the square numbers from 1 to 10.
Create a standalone program (whose name is specified by NAME-OF-STANDALONE-PROGRAM) from the yabasic-program, that is specified on the commandline. See the section about creating a standalone-program for details.
Change the infolevel of yabasic where INFOLEVEL can be one of debug, note, warning, error and fatal (the default is warning). This option changes the amount of debugging-information yabasic produces. However, normally only the author of yabasic (me !) would want to change this.
Print the embedded documentation of the named program. The embedded documentation of a program consists of all the comments within the program, which start with the special keyword doc.
Change the directory from which libraries will be imported (with the import-command). See also this entry for more information about the way, libraries will be searched.
If you want to set some options once for all, you may put them into your X-Windows resource file. This is usually the file .Xresources or some such within your home directory (type man X for details).
Here is a sample section, which may appear within this file:
yabasic*foreground: blue yabasic*background: gold yabasic*geometry: +10+10 yabasic*font: 9x15
This will set the foreground color of the graphic-window to blue and the background color to gold. The window will appear at position 10,10 and the text font will be 9x15.
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This chapter has sections for some of the major features of yabasic and names a few commands related with each area. So, depending on your interest, you find the most important commands of this area named; the other commands from this area may then be discovered through the links in the see also-section.
The print-command is used to put text on the text screen. Here, the term text screen stands for your terminal (under Unix) or the console window (under Windows).
At the bottom line, print simply outputs its argument to the text window. However, once you have called clear screen you may use advanced features like printing colors or copying areas of text with getscreen$ or putscreen.
You may ask the user for input with the input-command; use inkey$ to get each key as soon as it is pressed.
Of course, yabasic has the goto- and gosub-statements; you may go to a label or a line number (which is just a special kind of label). goto, despite its bad reputation ([goto considered harmful]), has still its good uses; however in many cases you are probably better off with loops like repeat-until, while-wend or do-loop; you may leave any of these loops with the break-statement or start the next iteration immediately with continue.
Decisions can be made with the if-statement, which comes either in a short and a long form. The short form has no then-keyword and extends up to the end of the line. The long form extends up to the final endif and may use some of the keywords then (which introduces the long form), else or elsif.
If you want to test the result of an expression against many different values, you should probably use the switch-statement.
You need to call open window before you may draw anything with either line, circle or rectangle; all of these statements may be decorated with clear or fill. Note however, that all graphics in yabasic is monochrome ("black on white"). Moreover, there can only be a single window open at any given moment in time.
Evyerything you have drawn can be send to your printer too, if you use the open printer command.
To allow for some (very) limited version of animated graphics, yabasic offers the commands getbit$ and putbit, which retrieve rectangular regions from the graphics-window into a string or vice versa.
If you want to sense mouse-clicks, you may use the inkey$-function.
Before you may read or write a file, you need to open it; once you are done, you should close it. Each open file is designated by a simple number, which might be stored within a variable and must be supplied if you want to access the file. This is simply done by putting a hash ('#') followd by the number of the file after the keyword input (for reading from) or print (for writing to a file) respectively.
If you need more control, you may consider reading and writing one byte at a time, using the multi-purpose commands peek and poke.
The best way to break any yabasic-program into smaller, more manageable chunks are subroutines and libraries. They are yabasic's most advanced means of structuring a program.
Subroutines are created with the command sub. they accept parameters and may return a value. Subroutines can be called much like any builtin function of yabasic; therefore they allow to extend the language itself.
Once you have created a set of related subroutines and you feel that they could be useful in other programs too, you may collect them into a library. Such a library is contained within a separate file and may be included in any of your programs, using the keyword import.
yabasic has the usual functions to extract parts from a string: left$, mid$ and right$. Note, that all of them can be assigned to, i.e. they may change part of a string.
If you want to split a string into tokens you should use the functions token or split.
There is quite a bunch of other string-processing functions like upper$ (converting to upper case), instr (finding one string within the other), chr$ (converting an ascii-code into a character), glob (testing a string against a pattern) and more. Just follow the links.
Yabasic handles numbers and arithmetic: You may calculate trigonometric functions like sin or atan, or logarithms (with log). Bitwise operations, like and or or are available as well min or max (calculate the minimum or maximum of its argument) or mod or int (reminder of a division or integer part or a number).
You may store data within your program within data-statements; during execution you will probably want to read it into arrays, which must have been dimed before.
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abs() — returns the absolute value of its numeric argument
y=abs(x)
If the argument of the abs-function is positive (e.g. 2) it is returned unchanged, if the argument is negative (e.g. -1) it is returned as a positive value (e.g. 1).
print abs(-2),abs(2)
This example will print 2 2
acos() — returns the arcus cosine of its numeric argument
x=acos(angle)
The acos is the arcus cosine-function, i.e. the inverse of the cos-function. Or, more elaborate: It Returns the angle (in radian, not degree !), which, fed to the cosine-function will produce the argument passed to the acos-function.
print acos(0.5),acos(cos(pi))
This example will print 1.0472 3.14159 which are π/3 and π respectively.
and — logical and, used in conditions
if (a and b) … while (a and b) …
Used in conditions (e.g within if, while or until) to join two expressions. Returns true, if and only if its left and right argument are both true and false otherwise.
Note, that logical shortcutsmay take place.
input "Please enter a number" a
if (a>=1 and a<=9) print "your input is between 1 and 9"
and() — the bitwise arithmetic and
x=and(a,b)
Used to compute the bitwise and of both its argument. Both arguments are treated as binary numbers (i.e. a series of 0 and 1); a bit of the resulting value will then be 1, if both arguments have a 1 at this position in their binary representation.
Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to and.
print and(6,3)
This will print 2. This result is clear, if you note, that the binary representation of 6 and 3 are 110 and 011 respectively; this will yield 010 in binary representaion or 2 as decimal.
arraydim() — returns the dimension of the array, which is passed as an array reference
a=arraydim(b())
If you apply the arraydim()-function on a one-dimensional array (i.e. a vector) it will return 1, on a two-dimensional array (i.e. a matrix) it will return 2, and so on.
This is mostly used within subroutines, which expect an array among their parameters. Such subroutines tend to use the arraydim-funtion to check, if the array which has been passed, has the right dimension. E.g. a subroutine to multiply two matrices may want to check, if it really is invoked with two 2-dimensional arrays.
dim a(10,10),b(10)
print arraydim(a()),arraydim(b())
This will print 2 1, which are the dimension of the arrays a() and b(). You may check out the function arraysize for a full-fledged example.
arraysize() — returns the size of a dimension of an array
x=arraysize(a(),b)
The arraysize-function computes the size of a specified dimension of a specified array. Here, size stands for the maximum number, that may be used as an index for this array. The first argument to this function must be an reference to an array, the second one specifies, which of the multiple dimensions of the array should be taken to calculate the size.
An Example involving subroutines: Let's say, an array has been declared as dim a(10,20) (that is a two-dimensional array or a matrix). If this array is passed as an array reference to a subroutine, this sub will not know, what sort of array has been passed. With the arraydim-function the sub will be able to find the dimension of the array, with the arraysize-function it will be able to find out the size of this array in its two dimensions, which will be 10 and 20 respectively.
Our sample array is two dimensional; if you envision it as a matrix this matrix has 10 lines and 20 columns (see the dim-statement above. To state it more formally: The first dimension (lines) has a size of 10, the second dimension (columns) has a size of 20; these mumbers are those returned by arraysize(a(),1) and arraysize(a(),2) respectively. Refer to the example below for a typical usage.
rem
rem This program adds two matrices elementwise.
rem
dim a(10,20),b(10,20),c(10,20)
rem initialization of the arrays a() and b()
for y=1 to 10:for x=1 to 20
a(y,x)=int(ran(4)):b(y,x)=int(ran(4))
next x:next y
matadd(a(),b(),c())
print "Result:"
for x=1 to 20
for y=10 to 1 step -1
print c(y,x)," ";
next y
print
next x
sub matadd(m1(),m2(),r())
rem This sub will add the matrices m1() and m2()
rem elementwise and store the result within r()
rem This is not very useful but easy to implement.
rem However, this sub excels in checking its arguments
rem with arraydim() and arraysize()
local x:local y
if (arraydim(m1())<>2 or arraydim(m2())<>2 or arraydim(r())<>2) then
error "Need two dimensional arrays as input"
endif
y=arraysize(m1(),1):x=arraysize(m1(),2)
if (arraysize(m2(),1)<>y or arraysize(m2(),2)<>x) then
error "The two matrices cannot be added elementwise"
endif
if (arraysize(r(),1)<>y or arraysize(r(),2)<>x) then
error "The result cannot be stored in the third argument"
endif
local xx:local yy
for xx=1 to x
for yy=1 to y
r(yy,xx)=m1(yy,xx)+m2(yy,xx)
next yy
next xx
end sub
asc() — accepts a string and returns the position of its first character within the ascii charset
a=asc(char$)
The asc-function accepts a string, takes its first character and looks it up within the ascii-charset; this position will be returned. The asc-function is the opposite of the chr$-function. There are valid uses for asc, however, comparing strings (i.e. to bring them into alphabetical sequence) is not among them; in such many cases you might consider to compare strings directly with <, = and > (rather than converting a string to a number and comparing this number).
input "Please enter a letter between 'a' and 'y': " a$
if (a$<"a" or a$>"y") print a$," is not in the proper range":end
print "The letter after ",a$," is ",chr$(asc(a$)+1)
asin() — returns the arcus sine of its numeric argument
angle=asin(x)
The acos is the arcus sine-function, i.e. the inverse of the sin-function. Or, more elaborate: It Returns the angle (in radian, not degree !), which, fed to the sine-function will produce the argument passed to the asin-function.
print asin(0.5),asin(sin(pi))
This will print 0.523599 -2.06823e-13 which is π and almost 0 respectively.
at() — can be used in the print-command to place the output at a specified position
clear screen … print at(a,b) print @(a,b)
The at-clause takes two numeric arguments (e.g. at(2,3)) and can be inserted after the print-keyword. at() can be used only if clear screen has been executed at least once within the program (otherwise you will get an error).
The two numeric arguments of the at-function may range from 0 to the width of your terminal minus 1, and from 0 to the height of your terminal minus 1; if any argument exceeds these values, it will be truncated accordingly. However, yabasic has no influence on the size of your terminal (80x25 is a common, but not mandatory), the size of your terminal and the maximum values acceptable within the at-clause may vary. To get the size of your terminal you may use the peek-function: peek("screenwidth") returns the width of your terminal and peek("screenheight") its height.
clear screen
maxx=peek("screenwidth")-1:maxy=peek("screenheight")-1
for x=0 to maxx
print at(x,maxy*(0.5+sin(2*pi*x/maxx)/2)) "*"
next x
This example plots a full period of the sine-function across the screen.
atan() — returns the arcus tangens of its numeric argument
angle=atan(a,b) angle=atan(a)
The atan is the arcus-tangens-function, i.e. the inverse of the tan-function. Or, more elaborate: It Returns the angle (in radian, not degree !), which, fed to the tan-function will produce the argument passed to the atan-function.
The atan-function has a second form, which accepts two arguments: atan(a,b) which is (mostly) equivilantly to atan(a/b) except for the fact, that the two-argument-form returns an angle in the range -π to π, whereas the one-argument-form returns an angle in the range -π/2 to π/2. To understand this you have to be good at math.
print atan(1),atan(tan(pi)),atan(-0,-1),atan(-0,1)
This will print 0.463648 2.06823e-13 -3.14159 3.14159 which is π/4, almost 0, -π and π respectively.
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beep — ring the bell within your computer; a synonym for bell
beep
The bell-command rings the bell within your computer once. This command is not a sound-interface, so you can neither vary the length or the height of the sound (technically, it just prints \a). bell is exactly the same as beep.
beep:print "This is a problem ..."
bell — ring the bell within your computer (just as beep)
bell
The beep-command rings the bell within your computer once. beep is a synonym for bell.
print "This is a problem ...":beep
bin$() — converts a number into a sequence of binary digits
hexadecimal$=bin$(decimal)
The bin$-function takes a single numeric argument an converts it into a string of binary digits (i.e. zeroes and ones). If you pass a negative number to bin$, the resulting string will be preceeded by a '-'.
If you want to convert the other way around (i.e. from binary to decimal) you may use the dec-function.
for a=1 to 100
print bin$(a)
next a
This example prints the binary representation of all digits between 1 and 100.
bind() — Binds a yabasic-program and the yabasic-interpreter together into a standalone program.
bind("foo.exe")The bind-command combines your own yabasic-program (plus all the libraries it does import) and the interpreter by copying them into a new file, whose name is passed as an argument. This new program may then be executed on any computer, even if it does not have yabasic installed.
Please see the section about creating a standalone-program for details.
if (!peek("isbound")) then
bind "foo"
print "Successfully created the standalone executable 'foo' !"
exit
endif
print "Hello World !"
This example creates a standalone program foo from itself.
The section about creating a standalone-program, the peek-function and the commandline options for Unix and Windows.
break — breaks out of a switch statement or a loop
break
break transfers control immediately outside the enclosing loop or switch statement. This is the preferred way of leaving a such a statement (rather than goto, which is still possible in most cases).
for a=1 to 10
break
print "Hi"
next a
while(1)
break
print "Hi"
wend
repeat
break
print "Hi"
until(0)
switch 1
case 1:break
case 2:case 3:print "Hi"
end switch
This example prints nothing at all, because each of the loops (and the switch-statement) does an immediate break (before it could print any "Hi").
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case — mark the different cases within a switch-statement
switch a case 1 case 2 … end switch … switch a$ case "a" case "b" … end switch
Please see the switch-statement.
input a
switch(a)
case 1:print "one":break
case 2:print "two":break
default:print "more"
end switch
Depending on your input (a number is expected) this code will print one or two or otherwise more.
chr$() — accepts a number and returns the character at this position within the ascii charset
character$=chr$(ascii)
The chr$-function is the opposite of the asc-function. It looks up and returns the character at the given position within the ascii-charset. It's typical use is to construct nonprintable characters which do not occur on your keyboard.
Nevertheless you won't use chr$ as often as you might think, because the most important nonprintable characters can be constructed using escape-sequences using the \-character (e.g. you might use \n instead of chr$(10) wherever you want to use the newline-character).
print "a",chr$(10),"b"
This will print the letters 'a' and 'b' in different lines because of the intervening newline-character, which is returned by chr$(10).
circle — draws a circle in the graphic-window
circle x,y,r clear circle x,y,r fill circle x,y,r clear fill circle x,y,r
The circle-command accepts three parameters: The x- and y-coordinates of the center and the radius of the circle.
Some more observations related with the circle-command:
The graphic-window must have been opened already.
The circle may well extend over the boundaries of the window.
If you have issued open printer before, the circle will finally appear in the printed hardcopy of the window.
fill circle will draw a filled (with black ink) circle.
clear circle will erase (or clear) the outline of the circle.
clear fill circle or fill clear circle will erase the full area of the circle.
open window 200,200
for n=1 to 2000
x=ran(200)
y=ran(200)
fill circle x,y,10
clear fill circle x,y,8
next n
This code will open a window and draw 2000 overlapping circles within. Each circle is drawn in two steps: First it is filled with black ink (fill circle x,y,10), then most of this circle is erased again (clear fill circle x,y,8). As a result each circle is drawn with an opaque white interior and a 2-pixel outline (2-pixel, because the radii differ by two).
clear — Erase circles or rectangles
clear rectangle 10,10,90,90 clear fill circle 50,50,20
May be used within the circle or rectangle command and causes these shapes to be erased (i.e. be drawn in the colour of the background).
fill can be used in conjunction with and whereever the fill-clause may appear. Used alone, clear will erase the outline (not the interior) of the shape (circle or rectangle); together with fill the whole shape (including its interior) is erased.
open window 200,200
fill circle 100,100,50
clear fill rectangle 10,10,90,90
This opens a window and draws a pacman-like figure.
clear screen — erases the text window
clear screen
clear screen erases the text window (the window where the output of print appears).
It must be issued at least once, before some advanced screen-commands (e.g. print at or inkey$) may be called; this requirement is due to some limititations of the curses-library, which is used by yabasic under Unix for some commands.
clear screen
print "Please press a key : ";
a$=inkey$
print a$
The clear screen command is essential here; if it would be omitted, yabasic would issue an error ("need to call 'clear screen' first") while trying to execute the inkey$-function.
clear window — clear the graphic window and begin a new page, if prining is under way
clear window
clear window clears the graphic window. If you have started prining the graphic via open printer, the clear window-command starts a new page as well.
open window 200,200
open printer "t.ps"
for a=1 to 10
if (a>1) clear window
text 100,100,"Hallo "+str$(a)
next a
close printer
close window
This example prints 10 pages, with the text "Hello 1", "Hello 2", … and so on. The clear screen-command clears the graphics window and starts a new page.
close — close a file, which has been opened before
close filenum close # filenum
The close-command closes an open file. You should issue this command as soon as you are done with reading from or writing to a file.
open "my.data" for reading as 1
input #1 a
print a
close 1
This program opens the file "my.data", reads a number from it, prints this number and closes the file again.
close curve — close a curve, that has been drawn by the line-command
new curve line to x1,y1 … close curve
The close curve-command closes a sequence of lines, that has been drawn by repeated line to-commands.
open window 200,200
new curve
line to 100,50
line to 150,150
line to 50,150
close curve
This example draws a triangle: The three line to-commands draw two lines; the final line is however not drawn explicitly, but drawn by the close curve-command.
close printer — stops printing of graphics
close printer
The close printer-command ends the printing graphics. Between open printer and close printer everything you draw (e.g. circles, lines …) is sent to your printer. close printer puts an end to printing and will make your printer eject the page.
open window 200,200
open printer
circle 100,100,50
close printer
close window
As soon as close printer is executed, your printer will eject a page with a circle on it.
close window — close the graphics-window
close window
The close window-command closes the graphics-window, i.e. it makes it disappear from your screen. It includes an implicit close printer, if a printer has been opened previously.
open window 200,200
circle 100,100,50
close window
This example will open a window, draw a circle and close the window again; all this without any pause or delay, so the window will be closed before you may regard the circle..
color — print with color
print color(fore$) text$ print color(fore$,back$) text$
Not a seperate command, but part of the print-command; may be included just after print and can only be issued after clear screen has been executed.
color() takes one or two string-arguments, specifying the color of the text and (optionally) the background.
The one or two strings passed to color() can be one of these: "black", "white", "red", "blue", "green", "yellow", "cyan" and "magenta" (which can be abbreviated as "bla", "whi", "red", "blu", "gre", "yel", "cya" and "mag" respectively).
color() can only be used, if clear scren has been issued at least once.
Note, that color() can be written as colour() too.
clear screen
dim col$(7):for a=0 to 7:read col$(a):next a
do
print color(col$(ran(7)),col$(ran(7))) " Hallo ";
pause 0.01
loop
data "black","white","red","blue"
data "green","yellow","cyan","magenta"
This prints the word " Hallo " in all colors accross your screen.
colour — see color
print colour(fore$) text$ print colour(fore$,back$) text$
compile — compile a string with yabasic-code on the fly
compile(code$)
This is an advanced command (closely related with the execute-command). It allows you to compile a string of yabasic-code (which is the only argument). Afterwards the compiled code is a normal part of your program.
Note, that there is no way to remove the compiled code.
compile("sub mysub(a):print a:end sub")
mysub(2)
This example creates a function named mysub, which simply prints its single argument.
continue — start the next iteration of a for-, do-, repeat- or while-loop
continue
You may use continue within any loop to start the next iteration immediately. Depending on the type of the loop, the loop-condition will or will not be checked. Especially: for- and while-loops will evaluate their respective conditions, do- and repeat-loops will not.
Remark: Another way to change the flow of execution within a loop, is the break-command.
for a=1 to 100
if mod(a,2)=0 continue
print a
next a
This example will print all odd numbers between 1 and 100.
Table of Contents
data — introduces a list of data-items
data 9,"world" … read b,a$
The data-keyword introduces a list of comma-seperated list of strings or numbers, which may be retrieved with the read-command.
The data-command itself does nothing; it just stores data. A single data-command may precede an arbitrarily long list of values, in which strings or numbers may be mixed at will.
yabasic internally uses a data-pointer to keep track of the current location within the data-list; this pointer may be reset with the restore-command.
do
restore
for a=1 to 4
read num$,num
print num$,"=",num
next a
loop
data "eleven",11,"twelve",12,"thirteen",13,"fourteen",14
This example just prints a series of lines eleven=11 up to fourteen=14 and so on without end.
The restore-command ensures that the list of data-items is read from the start with every iteration.
date$ — returns a string with various components of the current date
a$=date$
The date$-function (which must be called without parantheses; i.e. date$() would be an error) returns a string containing various components of a date; an example would be 4-05-27-2004-Thu-May. This string consists of various fields seperated by hyphens ("-"):
The day within the week as a number in the range 0 (=sunday) to 6 (=saturday) (in the example above: 4, i.e. thursday).
The month as a number in the range 1 (=january) to 12 (=december) (in the example: 5 which stands for may).
The day within the month as a number in the range 1 to 31 (in the example: 27).
The full, 4-digit year (in the example: 2004, which reminds me that I should adjust the clock within my computer …).
The abbreviated name of the day within the week (Mon to Sun).
The abbreviated name of the month (Jan to Dec).
Therefore the whole example above (4-05-27-2004-Thu-May) would read: day 4 in the week (counting from 0), May 27 in the year 2004, which is a thursday in May.
Note, that all fields within the string returned by date$ have a fixed with (numbers are padded with zeroes); therefore it is easy to extract the various fields of a date format with mid$.
rem Two ways to print the same ...
print mid$(date$,3,10)
dim fields$(6)
a=split(date$,fields$(),"-")
print fields$(2),"-",fields$(3),"-",fields$(4)
This example shows two different techniques to extract components from the value returned by date$. The mid$-function is the preferred way, but you could just as well split the return-value of date$ at every "-" and store the result within an array of strings.
dec() — convert a base 2 or base 16 number into decimal form
a=dec(number$) a=dec(number$,base)
The dec-function takes the string-representation of a base-2 or base-16 (which is the default) number and converts it into a decimal number. The optional second argument (base) might be used to specify a base other than 16. However, currently only base 2 or base 16 are supported.
input "Please enter a binary number: " a$
print a$," is ",dec(a$)
default — mark the default-branch within a switch-statement
switch a+3 case 1 … case 2 … default … end switch
The default-clause is an optional part of the switch-statement (see there for more information). It introduces a series of statements, that should be executed, if none of the casese matches, that have been specified before (each with its own case-clause).
So default specifies a default to be executed, if none of the explicitly named cases matches; hence its name.
print "Please enter a number between 0 and 6,"
print "specifying a day in the week."
input d
switch d
case 0:print "Monday":break
case 1:print "Tuesday":break
case 2:print "Wednesday":break
case 3:print "Thursday":break
case 4:print "Friday":break
case 5:print "Saturday":break
case 6:print "Sunday":break
default:print "Hey you entered something invalid !"
end switch
This program translates a number between 0 and 6 into the name of a weekday; the default-case is used to detect (and complain about) invalid input.
dim — create an array prior to its first use
dim array(x,y) dim array$(x,y)
The dim-command prepares one or more arrays (of either strings or numbers) for later use. This command can also be used to enlarges an existing array.
When an array is created with the dim-statement, memory is allocated and all elements are initialized with either 0 (for numerical arrays) or "" (for string arrays).
If the array already existed, and the dim-statement specifies a larger size than the current size, the array is enlarged and any old content is preserved.
Note, that dim cannot be used to shrink an array: If you specify a size, that is smaller than the current size, the dim-command does nothing.
Finally: To create an array, that is only known within a single subroutine, you should use the command local, which creates local variables as well as local arrays.
dim a(5,5)
for x=1 to 5:for y=1 to 5
a(x,y)=int(ran(100))
next y:next x
printmatrix(a())
dim a(7,7)
printmatrix(a())
sub printmatrix(ar())
local x,y,p,q
x=arraysize(ar(),1)
y=arraysize(ar(),2)
for q=1 to y
for p=1 to y
print ar(p,q),"\t";
next p
print
next q
end sub
This example creates a 2-dimenional array (i.e. a matrix) with the dim-statement and fills it with random numbers. The second dim-statement enlarges the array, all new elements are filled with 0.
The subroutine printmatrix just does, what its name says.
do — start a (conditionless) do-loop
do … loop
Starts a loop, which is terminated by loop; everything between do and loop will be repeated forever. This loop has no condition, so it is an infinite loop; note however, that a break- or goto-statement might be used to leave this loop anytime.
do
a=a+1
print a
if (a>100) break
loop
This example prints the numbers between 1 and 101. The break-statement is used to leave the loop.
doc — special comment, which might be retrieved by the program itself
doc This is a comment docu This is another comment
Introduces a comment, which spans up to the end of the line. But other than the rem-comment, any docu-comment is collected within the special docu$-array and might be retrieved later on. Moreover you might invoke yabasic -docu foo.yab on the commandline to retrieve the embedded documentation within the program foo.yab.
Instead of doc you may just as well write docu or even documentation.
rem Hi, this has been written by me
rem
doc This program asks for a number and
doc prints this number multiplied with 2
rem
rem Print out rhe above message
for a=1 to arraysize(docu$()):print docu$(a):next a
rem Read and print the number
input "Please input a number: " x
print x*2
This program uses the comments within its code to print out a help message for the user.
The contents of the doc-lines are retrieved from the docu$-array; if you do not want a comment to be collected within this array, use the rem-statement instead.
docu$ — special array, containing the contents of all docu-statement within the program
a$=docu$(1)
Before your program is executed, yabasic collects the content of all the doc-statements within your program within this 1-dimensional array (well only those within the main-program, libraries are skipped).
You may use the arraysize function to find out, how many lines it contains.
docu
docu This program reads two numbers
docu and adds them.
docu
rem retrieve and print the embedded documentation
for a=1 to arraysize(docu$(),1)
print docu$(a)
next a
input "First number: " b
input "Second number: " c
print "The sum of ",b," and ",c," is ",b+c
This program uses the embedded documentation to issue a usage-message.
dot — draw a dot in the graphic-window
dot x,y clear dot x,y
Draws a dot at the specified coordinates within your graphic-window. If printing is in effect, the dot appears on your printout too.
Use the functions peek("winheight") or peek("winwidth") to get the size of your window and hence the boundaries of the coordinates specified for the dot-command.
open window 200,200
circle 100,100,100
do
x=ran(200):y=ran(200)
dot x,y
total=total+1
if (sqrt((x-100)^2+(y-100)^2)<100) in=in+1
print 4*in/total
loop
This program uses a well known algorithm to compute π.
Table of Contents
else — mark an alternative within an if-statement
if (…) then … else … endif
The else-statement introduces the alternate branch of an if-statement. I.e. it starts the sequence of statements, which is executed, if the condition of the if-statement is not true.
input "Please enter a number: " a
if (mod(a,2)=1) then
print a," is odd."
else
print a," is even."
endif
This program detects, if the number you have entered is even or odd.
elsif — starts an alternate condition within an if-statement
if (…) then … elseif (…) … elsif (…) then … else … endif
The elsif-statement is used to select a single alternative among a series of choices.
With each elsif-statement you may specify a condition, which is tested, if the main condition (specified with the if-statement) has failed. Note that elsif might be just as well written as elseif.
Within the example below, two variables a and b are tested against a range of values. The variable a is tested with the elsif-statement. The very same tests are performed for the variable b too; but here an involved series of if-else-statements is employed, making the tests much more obscure.
input "Please enter a number: " a
if (a<0) then
print "less than 0"
elseif (a<=10) then
print "between 0 and 10"
elsif (a<=20)
print "between 11 and 20"
else
print "over 20"
endif
input "Please enter another number: " b
if (b<0) then
print "less than 0"
else
if (b<=10) then
print "between 0 and 10"
else
if (b<=20) then
print "between 11 and 20"
else
print "over 20"
endif
endif
endif
Note, that the very same tests are performed for the variables a and b, but can be stated much more clearly with the elsif-statement.
Note, that elsif might be written as elseif too, and that the keyword then is optional.
end — terminate your program
end
Terminate your program. Much (but not exactly) like the exit command.
Note, that end may not end your program immediately; if you have opened a window or called clear screen, yabasic assumes, that your user wants to study the output of your program after it has ended; therfore it issues the line ---Program done, press RETURN--- and waits for a key to be pressed. If you do not like this behaviour, consider using exit.
print "Do you want to continue ?"
input "Please answer y(es) or n(o): " a$
if (lower$(left$(a$,1))="n") then
print "bye"
end
fi
endif — ends an if-statement
if (…) then … endif
The endif-statement closes (or ends) an if-statement.
Note, that endif may be written in a variety of other ways: end if, end-if or even fi.
The endif-statement must be omitted, if the if-statement does not contain the keyword then (see the example below). Such an if-statement without endif extends only over a single line.
input "A number please: " a
if (a<10) then
print "Your number is less than 10."
endif
REM and now without endif
input "A number please: " a
if (a<10) print "Your number is less than 10."
end sub — ends a subroutine definition
sub foo(…) … end sub
Marks the end of a subroutine-definition (which starts with the sub-keyword). The whole concept of subroutines is explained within the entry for sub.
print foo(3)
sub foo(a)
return a*2
end sub
This program prints out 6. The subroutine foo simply returns twice its argument.
eof — check, if an open file contains data
open 1,"foo.bar" if (eof(1)) then … end if
The eof-function checks, if there is still data left within an open file. As an argument it expects the file-number as returned by (or used within) the open-function (or statement).
a=open("foo.bar")
while(not eof(a))
input #a,a$
print a$
end while
This example will print the contents of the file "foo.bar". The eof-function will terminate the loop, if there is no more data left within the file.
eor() — compute the bitwise exclusive or of its two arguments
print eor(a,b)
The eor-function takes two arguments and computes their bitwise exclusive or. See your favorite introductory text on informatics for an explanation of this function.
The xor-function is the same as the eor function; both are synonymous; however they have each their own description, so you may check out the entry of xor for a slightly different view.
for a=0 to 3
for b=0 to 3
print fill$(bin$(a))," eor ",fill$(bin$(b))," = ",fill$(bin$(eor(a,b)))
next b
next a
sub fill$(a$)
return right$("0"+a$,2)
end sub
This example prints a table, from which you may figure, how the eor-function is computed.
error — raise an error and terminate your program
error "Wrong, wrong, wrong !!"
Produces the same kind or error messages, that yabasic itself produces (e.g. in case of a syntax-error). The single argument is issued along with the current line-number.
input "Please enter a number between 1 and 10: " a
if (a<1 or a>10) error "Oh no ..."
This program is very harsh in checking the users input; instead of just asking again, the program terminates with an error, if the user enters something wrong.
The error message would look like this:
---Error in t.yab, line 2: Oh no ... ---Error: Program stopped due to an error
Well, there should be a corresponding called warning; unfortunately ther is none yet.
euler — another name for the constant 2.71828182864
foo=euler
euler is the well known constant named after Leonard Euler; its value is 2.71828182864. euler is not a function, so parens are not allowed (i.e. euler() will produce an error). Finally, you may not assign to euler; it wouldn't sense anyway, because it is a constant.
print euler
execute$() — execute a user defined subroutine, which must return a string
print execute$("foo$","arg1","arg2")execute$ can be used to execute a user defined subroutine, whose name may be specified as a string expression.
This feature is the only way to execute a subroutine, whose name is not known by the time you write your program. This might happen, if you want to execute a subroutine, which is compiled (using the compile command) during the course of execution of your program.
Note however, that the execute$-function is not the preferred method to execute a user defined subroutine; almost all cases you should just execute a subroutine by writing down its name within your yabasic program (see the example).
print execute$("foo$","Hello","world !")
sub foo$(a$,b$)
return a$+" "+b$
end sub
The example simply prints Hello world !, which is the return value of the user defined subroutine foo$. The same could be achieved by executing:
print foo$(a$,b$)
execute() — execute a user defined subroutine, which must return a number
print execute("bar","arg1","arg2")The execute-function is the counterpart of the execute$-function (please see there for some caveats). execute executes subroutines, which returns a number.
print execute("bar",2,3)
sub bar(a,b)
return a+b
end sub
exit — terminate your program
exit exit 1
Terminate your program and return any given value to the operating system. exit is similar to end, but it will terminate your program immediately, no matter what.
print "Do you want to continue ?"
input "Please answer y(es) or n(o): " a$
if (lower$(left$(a$,1))="n") exit 1
exp() — compute the exponential function of its single argument
foo=exp(bar)
This function computes e to the power of its argument, where e is the well known euler constant 2.71828182864.
The exp-function is the inverse of the log-function.
open window 100,100
for x=0 to 100
dot x,100-100*exp(x/100)/euler
next x
This program plots part of the exp-function, however the range is rather small, so that you may not recognize the function from this plot.
export — mark a function as globally visible
export sub foo(bar) … end sub
The export-statement is used within libraries to mark a user defined subroutine as visible outside the library wherein it is defined. Subroutines, which are not exported, must be qualified with the name of the library, e.g. foo.baz (where foo is the name of the library and baz the name of the subroutine); exported subroutines may be used without specifying the name of the library, e.g. bar.
Therefore export may only be useful within libraries.
The library foo.bar (which is listed below) defines two functions bar and baz, however only the function bar is exported and therefore visible even outside the library; baz is not exported and may only be used within the library foo.yab:
export sub bar()
print "Hello"
end sub
sub baz()
print "World"
end sub
Now within your main program cux.yab (which imports the library foo.yab); note that this program produces an error:
import foo print "Calling subroutine foo.bar (okay) ..." foo.bar() print "done." print "Calling subroutine bar (okay) ..." bar() print "done." print "Calling subroutine foo.baz (okay) ..." foo.baz() print "done." print "Calling subroutine baz (NOT okay) ..." baz() print "done."
The output when executing yabasic foo.yab is this:
Calling subroutine foo.bar (okay) ... Hello done. Calling subroutine bar (okay) ... Hello done. Calling subroutine foo.baz (okay) ... World done. Calling subroutine baz (NOT okay) ... ---Error in main.yab, line 16: can't find subroutine 'baz' ---Dump: sub baz() called in main.yab,16 ---Error: Program stopped due to an error
As the error message above shows, the subroutine baz must be qualified with the name of the library, if used outside the library, wherein it is defined (e.g. foo.baz. I.e. outside the library foo.yab you need to write foo.baz. baz alone would be an error.
The subroutine bar (without adding the name of the library) however may (and probably should) be used in any program, which imports the library foo.yab.
In some sense the set of exported subroutines constitutes the interface of a library.
Table of Contents
false — a constant with the value of 0
okay=false
The constant false can be assigned to variables which later appear in conditions (e.g. within an if-statement.
false may also be written as FALSE or even FaLsE.
input "Please enter a number between 1 and 10: " a
if (check_input(a)) print "Okay"
sub check_input(x)
if (x>10 or x<1) return false
return true
end sub
The subroutine check_input checks its argument and returns true or false according to the outcome of the check..
fi — another name for endif
if (…) … fi
fi marks the end of an if-statement and is exactly equivilent to endif, please see there for further information.
input "A number please: " a
if (a<10) then
print "Your number is less than 10."
fi
fill — draw a filled circles or rectangles
fill rectangle 10,10,90,90 fill circle 50,50,20
The keyword fill may be used within the circle or rectangle command and causes these shapes to be filled.
fill can be used in conjunction with and whereever the clear-clause may appear. Used alone, fill will fill the interior of the shape (circle or rectangle); together with clear the whole shape (including its interior) is erased.
open window 200,200
fill circle 100,100,50
clear fill rectangle 10,10,90,90
This opens a window and draws a pacman-like figure.
for — starts a for-loop
for a=1 to 100 step 2 … next a
The for-loop lets its numerical variable (a in the synopsis) assume all values within the given range. The optional step-clause may specify a value (default: 1) by which the variable will be incremented (or decremented, if step is negative).
Any for-statement can be replaced by a set of ifs and gotos; as you may infer from the example below this is normally not feasable. However if you want to know in detail how the for-statement works, you should study this example, which presents a for-statement and an exactly equivilant series of ifs and gotos.
for a=1 to 10 step 2:print a:next
a=1
label check
if (a>10) goto done
print a
a=a+2
goto check
label done
This example simply prints the numbers 1, 3, 5, 7 and 9. It does this twice: First with a simple for-statment and then with ifs and gotos.
frac() — return the fractional part of its numeric argument
x=frac(y)
The frac-function takes its argument, removes all the digits to the left of the comma and just returns the digits right of the comma, i.e. the fractional part.
Refer to the example to learn how to rewrite frac by employing the int-function.
for a=1 to 10
print frac(sqr(a))
print sqr(a)-int(sqr(a))
next a
The example prints the fractional part of the square root of the numbers between 1 and 10. Each result is computed (and printed) twice: Once by employing the frac-function and once by employing the int-function.
Table of Contents
getbit$() — return a string representing the bit pattern of a rectangle within the graphic window
a$=getbit$(10,10,20,20) a$=getbit$(10,10 to 20,20)
The function getbit returns a string, which contains the encoded bit-pattern of a rectangle within graphic window; the four arguments represent the borders of the rectangle. The string returned might later be fed to the putbit-command.
The getbit$-function might be used for simple animations (as in the example below).
open window 40,40
fill circle 20,20,18
circle$=getbit$(0,0,40,40)
close window
open window 200,200
for x=1 to 200
putbit circle$,x,80
next x
This example features a circle moving from left to right over the window.
getscreen$() — returns a string representing a rectangular section of the text terminal
a$=getscreen$(2,2,20,20)
The getscreen$ function returns a string representing the area of the screen as specified by its four arguments (which specify two corners). I.e. everything you have printed within this rectangle will be encoded in the string returned (including any colour-information).
Like most other commands dealing with advanced text output, getscreen$ requires, that you have called clear screen before.
clear screen
for a=1 to 1000:
print color("red") "1";
print color("green") "2";
print color("blue") "3";
next a
screen$=getscreen$(10,10,40,10)
print at(10,10) " Please Press 'y' or 'n' ! "
a$=inkey$
putscreen screen$,10,10
This program fills the screen with coloured digits and afterwards asks the user for a choice ( Please press 'y' or 'n' ! ). Afterwards the area of the screen, which has been overwritten by the question will be restored with its previous contents, whhch had been saved via getscreen$.
putscreen$
glob() — check if a string matches a simple pattern
if (glob(string$,pattern$)) …
The glob-function takes two arguments, a string and a (glob-) pattern, and checks if the string matches the pattern. However glob does not employ the powerful rules of regular expressions; rather it has only two special characters: * (which matches any number (even zero) of characters) and ? (which matches exactly a single character).
for a=1 to 10
read string$,pattern$
if (glob(string$,pattern$)) then
print string$," matches ",pattern$
else
print string$," does not match ",pattern$
endif
next a
data "abc","a*"
data "abc","a?"
data "abc","a??"
data "abc","*b*"
data "abc","*"
data "abc","???"
data "abc","?"
data "abc","*c"
data "abc","A*"
data "abc","????"
This program checks the string abc against various patterns and prints the result. The output is:
abc matches a* abc does not match a? abc matches a?? abc matches *b* abc matches * abc matches ??? abc does not match ? abc matches *c abc does not match A* abc does not match ????
There are no related commands.
gosub — continue execution at another point within your program (and return later)
gosub foo … label foo … return
gosub remembers the current position within your program and then passes the flow of execution to another point (which is normally marked with a label). Later, when a return-statement is encountered, the execution is resumed at the previous location.
gosub is the traditional command for calling code, which needs to be executed from various places within your program. However, with subroutines yabasic offers a much more flexible way to achieve this (and more). Therefore gosub must to be considered obsolete.
print "Do you want to exit ? "
gosub ask
if (r$="y") exit
label ask
input "Please answer yes or no, by typing 'y' or 'n': ",r$
return
goto — continue execution at another point within your program (and never come back)
goto foo … label foo
The goto-statement passes the flow of execution to another point within your program (which is normally marked with a label).
goto is normally considered obsolete and harmful, however in yabasic it may be put to the good use of leaving loops (e.g. while or for) prematurely. Note however, that subroutines may not be left with the goto-statement.
print "Please press any key to continue."
print "(program will continue by itself within 10 seconds)"
for a=1 to 10
if (inkey$(1)<>"") then goto done
next a
label done
print "Hello World !"
Here the goto-statment is used to leave the for-loop prematurely.
Table of Contents
hex$() — convert a number into hexadecimal
print hex$(foo)
The hex$-function converts a number into a string with its hexadecimal representation. hex$ is the inverse of the dec-function.
open 1,"foo"
while(!eof(1))
print right$("0"+hex$(peek(1)),2)," ";
i=i+1
if (mod(i,10)=0) print
end while
print
This program reads the file foo and prints its output as a hex-dump using the hex-function.
Table of Contents
if — evaluate a condition and execute statements or not, depending on the result
if (…) then … endif if (…) … if (…) then … else … endif if (…) then … elsif (…) … elsif (…) then … else … endif
The if-statement is used to evaluate a conditions and take actions accordingly. (As an aside, please note that there is no real difference between conditions and expressions.)
There are two major forms of the if-statement:
The one-line-form without the keyword then:
if (…) …This form evaluates the condition and if the result is true executes all commands (seperated by colons) upt to the end of the line. There is neither an endif keyword nor an else-branch.
The multi-line-form with the keyword then:
if (…) then … elsif (…) … else … endif(where elsif and else are optional, whereas endif is not.
According to the requirements of your program, you may specify:
elsif(…), which specifies a condition, that will be evaluated only if the condition(s) whithin if or any preceeding elsif did not match.
else, which introduces a sequence of commands, that will be executed, if none of the conditions above did match.
endif is required and ends the if-statement.
input "Please enter a number between 1 and 4: " a
if (a<=1 or a>=4) error "Wrong, wrong !"
if (a=1) then
print "one"
elsif (a=2)
print "two"
elsif (a=3)
print "three"
else
print "four"
endif
The input-number between 1 and 4 is simply echoed as text (one, two, …). The example demonstrates both forms (short and long) of the if-statement (Note however, that the same thing can be done, probably somewhat more elegant, with the switch-statement).
import — import a library
import foo
The import-statment imports a library. It expects a single argument, which must be the name of a library (without the trailing .yab). This library will then be read and parsed and its subroutines (and variables) will be made available within the main program.
Libraries will first be searched within the current directory (i.e. the directory within which you have invoked yabasic), then within a special directory, whose exact location depends on your system. Typical values would be /usr/lib under Unix or C:\yabasic\lib under Windows. However only yabasic -help-usage may tell the truth. The location of this second directory may be changed with the option -library (either under Windows or Unix).
Lets say you have a yabasic-program foo.yab, which imports a library lib.yab. foo.yab reads:
import lib
rem This works ...
lib.x(0)
rem This works too ..
x(1)
rem And this.
lib.y(2)
rem But this not !
y(3)
Now the library lib.yab reads:
rem Make the subroutine x easily available outside this library export sub x(a) print a return end sub rem sub y must be referenced by its full name rem outside this library sub y(a) print a return end sub
This program produces an error:
0 1 2 ---Error in foo.yab, line 13: can't find subroutine 'y' ---Dump: sub y() called in foo.yab,13 ---Error: Program stopped due to an errorAs you may see from the error message, yabasic is unable to find the subroutine y without specifying the name of the library (i.e. lib.y). The reason for this is, that y, other than x, is not exported from the library lib.yab (using the export-statement).
inkey$ — wait, until a key is pressed
clear screen foo$=inkey$ inkey$ foo$=inkey$(bar) inkey$(bar)
The inkeys$-function waits, until the user presses a key on the keyboard or a button of his mouse, and returns this very key. An optional argument specifies the number of seconds to wait; if omitted, inkey$ will wait indefinitely.
inkey$ may only be used, if clear screen has been called at least once.
For normal keys, yabasic simply returns the key, e.g. a, 1 or !. For function keys you will get f1, f2 and so on. Other special keys will return these strings respectively: enter, backspace, del, esc, scrnup (for screen up), scrndown and tab. Modifier keys (e.g. ctrl, alt or shift) by themself can not be detected (however, if you press shift and e.g. a simultaniously, inkey$ will return the letter A instead of a of course).
If a graphical window has been opened (via open window) any mouseclick within this window will be returned by inkey$ too. The string returned (e.g. MB1d+0:0028,0061, MB2u+0:0028,0061 or MB1d+1:0028,0061) is constructed as follows:
Every string associated with a mouseclick will start with the fixed string MB
The next digit (1, 2 or 3) specifies the mousebutton pressed.
A single letter, d or u, specifies, if the mousebutton has been pressed or released: d stands for down, i.e. the mousebutton has been pressed; u means up, i.e. the mousebutton has been released.
The plus-sign ('+'), which follows is always fixed.
The next digit (in the range 0 to 7) encodes the modifier keys pressed, where 1 stands for shift, 2 stands for alt and 4 stands for ctrl.
The next four digits (e.g. 0028) contain the x-position, where the mousebutton has been pressed.
The comma to follow is always fixed.
The last four digits (e.g. 0061) contain the y-position, where the mousebutton has been pressed.
All those fields are of fixed length, so you may use functions like mid$ to extract certain fields. However, note that with mousex, mousey, mouseb and mousemod there are specialized functions to return detailed information about the mouseclick. Finally it should be noted, that inkey$ will only register mouseclicks within the graphic-window; mouseclicks in the text-window cannot be detected.
inkey$ accepts an optional argument, specifying a timeout in seconds; if no key has been pressed within this span of time, an empty string is returned. If the timeout-argument is omitted, inkey$ will wait for ever.
clear screen
open window 100,100
print "Press any key or press 'q' to stop."
repeat
a$=inkey$
print a$
until(a$="q")
This program simply returns the key pressed. You may use it, to learn, which strings are returned for the special keys on your keyboard (e.g. function-keys).
input — read input from the user (or from a file) and assign it to a variable
input a input a,b,c input a$ input "Hello" a input #1 a$
input reads the new contents of one or many (numeric- or string-) variables, either from the keyboard (i.e. from you) or from a file. An optional first string-argument specifies a prompt, which will be issued before reading any contents.
If you want to read from an open file, you need to specify a hash ('#'), followed by the number, under which the file has been opened.
Note, that the input is split at spaces, i.e. if you enter a whole line consisting of many space-seperated word, the first input-statement will only return the first word; the other words will only be returned on subsequent calls to input; the same applies, if a single input reads multiple variables: The first variable gets only the first word, the second one the second word, and so on. If you don't like this behaviour, you may use line input, which returns a whole line (including embedded spaces) at once.
input "Please enter the name of a file to read: " a$
open 1,a$
while(!eof(1))
input #1 b$
print b$
wend
If this program is stored within a file test.yab and you enter this name when prompted for a file to read, you will see this output:
Please enter the name of a file to read: t.yab input "Please enter the name of a file to read: " a$ open 1,a$ while(!eof(1)) input #1 b$ print b$ wend
instr() — searches its second argument within the first; returns its position if found
print instr(a$,b$) if (instr(a$,b$)) … pos=instr(a$,b$,x)
The instr-functions requires two string arguments and searches the second argument within the first. If the second argument can be found within the first, the position is returned (counting from one). If it can not be found, the instr-function returns 0; this makes this function usable within the condition of an if-statement (see the example below).
If you supply a third, numeric argument to the instr-function, it will be used as a starting point for the search. Therefore instr("abcdeabcdeabcde","e",8) will return 10, because the search for an "e" starts at position 8 and finds the "e" at position 10 (and not the one at position 5).
input "Please enter a text containing the string 'bumf': " a$
if (instr(a$,"bumf")) then
print "Well done !"
else
print "not so well ..."
endif
int() — return the integer part of its single numeric argument
print int(a)
The int-function returns only the digits before the comma; int(2.5) returns 2 and int(-2.3) returns -2.
input "Please enter a whole number between 1 and 10: " a
if (a=int(a) and a>=1 and a<=10) then
print "Thanx !"
else
print "Never mind ..."
endif
Table of Contents
label — mark a specific location within your program for goto, gosub or restore
label foo … goto foo
The label-command can be used to give a name to a specific location within your program. Such a position might be referred from one of three commands: goto, gosub and restore.
You may use labels safely within libraries, because a label (e.g. foo) does not collide with a label with the same name within the main program or within another library; yabasic will not mix them up.
As an aside, please note, that line numbers are a special (however deprecated) case of labels; see the second example below.
for a=1 to 100
if (rand(10)>5) goto done
next a
label done
10 for a=1 to 100
20 if (rand(10)>5) goto 40
30 next a
40
Within this example, the for-loop will probably be left prematurely with a goto-statement. This task is done twice: First with labels and then again with line numbers.
left$() — return (or change) left end of a string
print left$(a$,2) left$(b$,3)="foobar"
The left$-function accepts two arguments (a string and a number) and returns the part from the left end of the string, whose length is specified by its second argument. Loosely spoken, it simply returns the requested number of chars from the left end of the given string.
Note, that the left$-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the left$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.
input "Please answer yes or no: " a$
l=len(a$):a$=lower$(a$):print "Your answer is ";
if (left$("yes",l)=a$ and l>=1) then
print "yes"
elsif (left$("no",l)=a$ and l>=1) then
print "no"
else
print "?"
endif
This example asks a simple yes/no question and goes some way to accept even incomplete input, while still beeing able to reject invalid input.
This second example demonstrates the capability to assign to the left$-function.
a$="Heiho World !" print a$ left$(a$,5)="Hello" print a$
len() — return the length of a string
x=len(a$)
The len-function returns the length of its single string argument.
input "Please enter a password: " a$
if (len(a$)<6) error "Password too short !"
This example checks the length of the password, that the user has entered.
line — draw a line
open window 100,100 line 0,0,100,100 line 0,0 to 100,100 new curve line 100,100 line to 100,100 open window 100,100 clear line 0,0,100,100 clear line 0,0 to 100,100 new curve clear line 100,100 clear line to 100,100
The line-command draws a line. Simple as this is, the line-command has a large variety of forms as they are listed in the synopsis above. Lets look at them a little closer:
A line has a starting and an end point; therefore the line-command (normally) needs four numbers as arguments, representing these two points. This is the first form appearing within the synopsis.
You may seperate the two points with either ',' or to, which accounts for the second form of the line-command.
The line-command may be used to draw a connected sequence of lines with a sequence of commands like line x,y; Each command will draw a line from the point where the last line-command left off, to the point specified in the arguments. Note, that you need to use the command new curve before you may issue such a line-command. See the example below.
You may insert the word to for beauty: line to x,y, which does exactly the same as line x,y
Finally, you may choose not to draw, but to erase the lines; this can be done by prepending the phrase clear. This account for all the other forms of the line-command.
open window 200,200
line 10,10 to 10,190
line 10,190 to 190,190
new curve
for a=0 to 360
line to 10+a*180/360,100+60*sin(a*pi/180)
next a
This example draws a sine-curve (with an offset in x- and y-direction). Note, that the first line-command after new curve does not draw anything. Only the coordinates will be stored. The second iteration of the loop then uses these coordinates as a starting point for the first line.
line input — read in a whole line of text and assign it to a variable
line input a line input a$ line input "Hello" a line input #1 a$
In most respects line input is like the input-command: It reads the new contents of a variable, either from keyboard or from a file. However, line input always reads a complete line and assigns it to its variable. line input does not stop reading at spaces and is therefore the best way to read in a string which might contain whitespace. Note, that the final newline is stripped of.
line input "Please enter your name (e.g. Frodo Beutelin): " a$
print "Hello ",a$
Note that the usage of line input is essential in this example; a simple input-statement would only return the string up to the first space, e.g. Frodo.
local — mark a variable as local to a subroutine
sub foo() local a,b,c$,d(10),e$(5,5) … end sub
The local-command can (and should be) used to mark a variable (or array) as local to the containing subroutine. This means, that a local variable in your subroutine is totally different from a variable with the same name within your main program. Variables which are known everywhere within your program are called global in contrast.
Declaring variables within the subroutine as local helps to avoid hard to find bugs; therefore local variables should be used whenever possible.
Note, that the parameters of your subroutines are always local.
As you may see from the example, local arrays may be created without using the keyword dim (which is required only for global arrays).
a=1
b=1
print a,b
foo()
print a,b
sub foo()
local a
a=2
b=2
end sub
This example demonstrates the difference between local and global variables; it produces this output:
1 1 1 2
As you may see, the content of the global variable a is unchanged after the subroutine foo; this is because the assignment a=2 within the subroutine affects the local variable a only and not the global one. However, the variable b is never declared local and therefore the subroutine changes the global variable, which is reflected in the output of the second print-statement.
log() — compute the natural logarithm
a=log(x) a=log(x,base)
The log-function computes the logarithm of its first argument. The optional second argument gives the base for the logarithm; if this second argument is omitted, the euler-constant 2.71828… will be taken as the base.
open window 200,200
for x=10 to 190 step 10:for y=10 to 190 step 10
r=3*log(1+x,1+y)
if (r>10) r=10
if (r<1) r=1
fill circle x,y,r
next y:next x
This draws another nice plot.
loop — marks the end of an infinite loop
do … loop
The loop-command marks the ends of a loop (which is started by do), wherein all statements within the loop are repeated forever. In this respect the do loop-loop is infinite, however, you may leave it anytime via break or goto.
print "Hello, I will throw dice, until I get a 2 ..."
do
r=int(rand(6))+1
print r
if (r=2) break
loop
lower$() — convert a string to lower case
l$=lower$(a$)
The lower$-function accepts a single string-argument and converts it to all lower case.
input "Please enter a password: " a$
if (a$=lower$(a$)) error "Your password is NOT mixed case !"
This example prompts for a password and checks, if it is really lower case.
ltrim$() — trim spaces at the left end of a string
a$=ltrim$(b$)
The ltrim$-function removes all whitespace from the left end of a string and returns the result.
input "Please answer 'yes' or 'no' : " a$
a$=lower$(ltrim$(rtrim$(a$)))
if (len(a$)>0 and a$=left$("yes",len(a$))) then
print "Yes ..."
else
print "No ..."
endif
This example prompts for an answer and removes any spaces, which might precede the input; therefore it is even prepared for the (albeit somewhat patological case, that the user first hits space before entering his answer.
Table of Contents
max() — return the larger of its two arguments
print max(a,b)
Return the maximum of its two arguments.
dim m(10)
for a=1 to 1000
m=0
For b=1 to 10
m=max(m,ran(10))
next b
m(m)=m(m)+1
next a
for a=1 to 9
print a,": ",m(a)
next a
Within the inner for-loop (the one with the loop-variable b), the example computes the maximum of 10 random numbers. The outer loop (with the loop variable a) now repeats this process 1000 times and counts, how often each maximum appears. The last loop finally reports the result.
Now, the interesting question would be, which will be approached, when we increase the number of iterations from thousend to infinity. Well, maybe someone could just tell me :-)
mid$() — return (or change) characters from within a string
print mid$(a$,2,1) print mid$(a$,2) mid$(a$,5,3)="foo" mid$(a$,5)="foo"
The mid$-function requires three arguments: a string and two numbers, where the first number specifies a position within the string and the second one gives the number of characters to be returned; if you omit the second argument, the mid$-function returns all characters up to the end of the string.
Note, that you may assign to the mid$-function, i.e. mid$ may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the mid$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.
input "Please enter a string: " a$
for a=1 to len(a$)
if (instr("aeiou",lower$(mid$(a$,a,1)))) mid$(a$,a,1)="e"
next a
print "When you turn everything to lower case and"
print "replace every vowel with 'e', your input reads:"
print
print a$
This example transforms the input string a bit, using the mid$-function to retrieve a character from within the string as well as to change it.
min() — return the smaller of its two arguments
print min(a,b)
Return the minimum of its two argument.
dim m(10)
for a=1 to 1000
m=min(ran(10),ran(10))
m(m)=m(m)+1
next a
for a=1 to 9
print a,": ",m(a)
next a
For each iteration of the loop, the lower of two random number is recorded. The result is printed at the end.
mod() — compute the remainder of a division
print mod(a,b)
The mod-function divides its two arguments and computes the remainder. Note, that a/b-int(a/b) and mod(a,b) are always equal.
clear screen
print at(10,10) "Please wait ";
p$="-\|/"
for a=1 to 100
rem ... do something lengthy here, or simply sleep :-)
pause(1)
print at(22,10) mid$(p$,1+mod(a,4))
next a
This example executes some time consuming action within a loop (in fact, it simply sleeps) and gives the user some indication of progress by displaying a turning bar (thats where the mod()-function comes into play).
mouseb — extract the state of the mousebuttons from a string returned by inkey$
inkey$ print mouseb() print mouseb a$=inkey$ print mouseb(a$)
The mouseb-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function. If a mousebutton has been pressed, the mouseb-function returns the number (1,2 or 3) of the mousebutton, when it is pressed and returns its negative (-1,-2 or -3), when it is released.
The mouseb-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mouseb is called without any arguments, it returns the values from the last call to inkey$, which are stored implicitly and internally by yabasic.
Note however, that the value returned by the mouseb-function does not reflect the current state of the mousebuttons. It rather extracts the information from the string passed as an argument (or from the last call to the inkey$-function, if no argument is passed). So the value returned by mouseb reflects the state of the mousebuttons at the time the inkey$-function has been called; as opposed to the time the mouseb-function is called.
open window 200,200
clear screen
print "Please draw lines; press (and keep it pressed)"
print "the left mousebutton for the starting point,"
print "release it for the end-point."
do
if (mouseb(release$)=1) press$=release$
release$=inkey$
if (mouseb(release$)=-1) then
line mousex(press$),mousey(press$) to mousex(release$),mousey(release$)
endif
loop
This is a maybe the most simplistic line-drawing program possible, catching presses as well as releases of the first mousebutton.
mousemod — return the state of the modifier keys during a mouseclick
inkey$ print mousemod() print mousemod a$=inkey$ print mousemod(a$)
The mousemod-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function if a mousebutton has been pressed. It returns the state of the keyboard modifiers (shift, ctrl or alt): If the shift-key is pressed, mousemod returns 1, for the alt-key 2 and for the ctrl-key 4. If more than one key is pressed, the sum of these values is returned, e.g. mousemod returns 5, if shift and ctrl are pressed simultanously.
The mousemod-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousemod is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).
Please see also the Note within the mouseb-function.
open window 200,200
clear screen
do
a$=inkey$
if (left$(a$,2)="MB") then
x=mousex(a$)
y=mousey(a$)
if (mousemod(a$)=0) then
circle x,y,20
else
fill circle x,y,20
endif
endif
loop
This program draws a circle, whenever a mousebutton is pressed; the circles are filled, when any modifier is pressed, and empty if not.
mousex — return the x-position of a mouseclick
inkey$ print mousex() print mousex a$=inkey$ print mousex(a$)
The mousex-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function; It returns the x-position of the mouse as encoded within its argument.
The mousex-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousex is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).
Please see also the Note within the mouseb-function.
open window 200,200
clear screen
do
a$=inkey$
if (left$(a$,2)="MB") then
line mousex,0 to mousex,200
endif
loop
This example draws vertical lines at the position, where the mousebutton has been pressed.
mousey — return the y-position of a mouseclick
inkey$ print mousey() print mousey a$=inkey$ print mousey(a$)
The mousey-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function. mousey returns the y-position of the mouse as encoded within its argument.
The mousey-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousey is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).
Please see also the Note within the mouseb-function.
open window 200,200
clear screen
do
a$=inkey$
if (left$(a$,2)="MB") then
line 0,mousey to 200,mousey
endif
loop
This example draws horizontal lines at the position, where the mousebutton has been pressed.
Table of Contents
new curve — start a new curve, that will be drawn with the line-command
new curve line to x,y
The new curve-function starts a new sequence of lines, that will be drawn by repeated line to-commands.
open window 200,200
ellipse(100,50,30,60)
ellipse(150,100,60,30)
sub ellipse(x,y,xr,yr)
new curve
for a=0 to 2*pi step 0.2
line to x+xr*cos(a),y+yr*sin(a)
next a
close curve
end sub
This example defines a subroutine ellipse that draws an ellipse. Within this subroutine, the ellipse is drawn as a sequence of lines started with the new curve command and closed with close curve.
next — mark the end of a for loop
for a=1 to 10 next a
The next-keyword marks the end of a for-loop. All statements up to the next-keyword will be repeated as specified with the for-clause. Note, that the name of the variable is optional; so instead of next a you may write next.
for a=1 to 300000
for b=1 to 21+20*sin(pi*a/20)
print "*";
next b
print
sleep 0.1
next a
This example simply plots a sine-curve until you fall asleep.
not — negate an expression; can be written as !
if (not a<b) then … bad=!okay
The keyword not (or ! for short) is mostly used within conditions (e.g. within if- or while-statements). There it is employed to negate the condition or expression (i.e. turn TRUE into FALSE and vice versa)
However not can be used within arithmetic calculations too., simply because there is no difference between arithmetic and logical expressions.
input "Please enter three ascending numbers: " a,b,c
if (not (a<b and b<c)) error " the numbers you have entered are not ascending ..."
numparams — return the number of parameters, that have been passed to a subroutine
sub foo(a,b,c) if (numparams=1) … … end sub
Within a subroutine the local variable numparam or numparams contains the number of parameters, that have been passed to the subroutine. This information can be useful, because the subroutine may have been called with fewer parameters than actually declared. The number of values that actually have been passed while calling the subroutine, can be found in numparams.
Note, that arguments which are used in the definition of a subroutine but are left out during a call to it (thereby reducing the value of numparams) receive a value of 0 or "" (empty string) respectively.
a$="123456789"
print part$(a$,4)
print part$(a$,3,7)
sub part$(a$,f,t)
if (numparams=2) then
return mid$(a$,f)
else
return mid$(a$,f,t-f+1)
end if
end sub
When you run this example, it will print 456789 and 34567. Take a look at the subroutine part$, which returns part of the string which has been passed as an argument. If (besides the string) two numbers are passed, they define the starting and end position of the substring, that will be returned. However, if only one number is passed, the rest of the string, starting from this position will be returned. Each of these cases is recognized with the help of the numparams variable.
Table of Contents
on goto — jump to one of multiple gosub-targets
on a gosub foo,bar,baz … label foo … return label bar … return label baz … return
The on gosub statement uses its numeric argument (the one between on and gosub) to select an element from the list of labels, which follows after the gosub-keyword: If the number is 1, the program does a gosub to the first label; if the number is 2, to the second and, so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.
Note, that the on gosub-command can no longer be considered state of the art; people (not me !) may even start to mock you, if you use it.
do
print "Please enter a number between 1 and 3: "
print
input "Your choice " a
on a gosub bad,one,two,three,bad
loop
label bad
print "No. Please between 1 and 3"
return
label one
print "one"
return
label two
print "two"
return
label three
print "three"
return
Note, how invalid input (a number less than 1, or larger than 3) is automatically detected.
on goto — jump to one of many goto-targets
on a goto foo,bar,baz … label foo … label bar … label baz …
The on goto statement uses its numeric argument (the one between on and goto to select an element from the list of labels, which follows after the goto-keyword: If the number is 1, the execution continues at the first label; if the number is 2, at the second, and so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.
Note, that (unlike the goto-command) the on goto-command can no longer be considered state of the art; people may (not me !) even start to mock you, if you use it.
label over
print "Please Select one of these choices: "
print
print " 1 -- show time"
print " 2 -- show date"
print " 3 -- exit"
print
input "Your choice " a
on a goto over,show_time,show_date,terminate,over
label show_time
print time$()
goto over
label show_date
print date$()
goto over
label terminate
exit
Note, how invalid input (a number less than 1, or larger than 3) is automatically detected; in such a case the question is simply issued again.
on interrupt — change reaction on keyboard interrupts
on interrupt break … on interrupt continue
With the on interrupt-command you may change the way, how yabasic reacts on a keyboard interrupt; it comes in two variants: on interrupt break and on interrupt continue. A keyboard interrupt is produced, if you press ctrl-C on your keyboard; normally (and certainly after you have called on interrupt break), yabasic will terminate with an error message. However after the command on interrupt continue yabasic ignores any keyboard interrupt. This may be useful, if you do not want your program beeing interruptible during certain critical operations (e.g. updating of files).
print "Please stand by while writing a file with random data ..."
on interrupt continue
open "random.data" for writing as #1
for a=1 to 100
print #1 ran(100)
print a," percent done."
sleep 1
next a
close #1
on interrupt continue
This program writes a file with 100 random numbers. The on interrupt continue command insures, that the program will not be terminated on a keyboard interrupt and the file will be written entirely in any case. The sleep-command just stretches the process arificially to give you a chance to try a ctrl-C.
There is no related command.
open — open a file
open a,"file","r"
open #a,"file","w"
open #a,printer
open "file" for reading as a
open "file" for writing as #a
a=open("file")
a=open("file","r")
if (open(a,"file")) …
if (open(a,"file","w")) …
The open-command opens a file for reading or writing or a printer for printing text. open comes in a wide variety of ways; it requires these arguments:
In the synopsis this is a or #a. In yabasic each file is associated with a number between 1 and a maximum value, which depends on the operating system. For historical reasons the filenumber can be preceded by a hash ('#'). Note, that specifying a filenumber is optional; if it is omitted, the open-function will return a filenumber, which should then be stored in a variable for later reference. This filenumber can be a simple number or an arbitrary complex arithmetic expression, in which case braces might be necessary to save yabasic from getting confused.
In the synopsis above this is "file". This string specifies the name of the file to open (note the important caveat on specifying these filenames).
In the synopsis this is "r", "w", for reading or for writing. This string or clause specifies the mode in which the file is opened; it may be one of:
Open the file for reading (may also be written as for reading). If the file does not exist, the command will fail. This mode is the default, i.e. if no mode is specified with the open-command, the file will be opened with this mode.
Open the file for writing (may also be written as for writing). If the file does not exist, it will be created.
Open the file for appending, i.e. what you write to the file will be appended after its initial contents. If the file does not exist, it will be created.
This letter may not appear alone, but may be combined with the other letters (e.g. "rb") to open a file in binary mode (as opposed to text mode).
As you may see from the synopsis, the open-command may either be called as a command (without braces) or as a function (with braces). If called as a function, it will return the filenumber or zero if the operation fails. Therefore the open-function may be used within the condition of an if-statement.
If the open-command fails, you may use peek("error") to retrieve the exact nature of the error.
Furthermore note, that there is another, somewhat separate usage of the open-command; if you specify the bareword printer instead of a filename, the command opens a printer for printing text. Every text (and only text) you print to this file will appear on your printer. Note, that this is very different from printing graphics, as can be done with open printer.
Finally you may read the description for peek("error") to learn which errors may have happened during an open-call.
open "foo.bar" for writing as #1
print #1 "Hallo !"
close #1
if (not open(1,"foo.bar")) error "Could not open 'foo.bar' for reading"
while(not eof(1))
line input #1 a$
print a$
wend
This example simply opens the file foo.bar, writes a single line, reopens it and reads its contents again.
close, print, peek, peek("error") and open printer
open printer — open printer for printing graphics
open printer open printer "file"
The open printer-command opens a printer for printing graphics. The command requires, that a graphic window has been opened before. Everything that is drawn into this window will then be sent to the printer too.
A new piece of paper may be started with the clear window-command; the final (or only) page will appear after the close printer-command.
Note, that you may specify a filename with open printer; in that case the printout will be sent to a filename instead to a printer. Your program or the user will be responsible for sending this file to the printer afterwards.
If you use yabasic under Unix, you will need a postscript printer (because yabasic produces postscript output). Alternatively you may use ghostscript to transfrom the postscript file into a form suitable for your printer; but that is beyond the responsibility of yabasic.
open window 200,200
open printer
line 0,0 to 200,200
text 100,100,"Hallo"
close window
close printer
This example will open a window, draw a line and print some text within; everything will appear on your printer too.
open window — open a graphic window
open window x,y open window x,y,"font"
The open window-command opens a window of the specified size. Only one window can be opened at any given moment of time.
An optional third argument specifies a font to be used for any text within the window. Please note, that if you open a window several times with varying font-arguments, only the first one will take effect, all others will be ignored; that means that you may onle use a single font for all windows in your program.
for a=200 to 400 step 10
open window a,a
for b=0 to a
line 0,b to a,b
line b,0 to b,a
sleep 0.1
close window
next a
or — logical or, used in conditions
if (a or b) … while (a or b) …
Used in conditions (e.g within if or while) to join two expressions. Returns true, if either its left or its right or both arguments are true; returns false otherwise.
input "Please enter a number"
if (a>9 or a<1) print "a is not between 1 and 9"
or() — arithmetic or, used for bit-operations
x=or(a,b)
Used to compute the bitwise or of both its argument. Both arguments are treated as binary numbers (i.e. a series of 0 and 1); a bit of the resulting value will then be 1, if any of its arguments has 1 at this position in their binary representation.
Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to or.
print or(14,3)
This will print 15. This result is clear, if you note, that the binary representation of 14 and 3 are 1110 and 0011 respectively; this will yield 1111 in binary representaion or 15 as decimal.
Table of Contents
pause — pause, sleep, wait for the specified number of seconds
pause 5
The pause-command has many different names: You may write pause, sleep or wait interchangable; whatever you write, yabasic will always do exactly the same.
The pause-command will simply wait for the specified number of seconds. This may be a fractional number, so you may well wait less than a second. However, if you try to pause for a smaller and smaller interval (e.g. 0.1 seconds, 0.01 seconds, 0.001 seconds and so on) you will find that at some point yabasic will not wait at all. The minimal interval that can be waited depends on the system (Unix, Windows) you are using.
The pause-command cannot be interrupted. However, sometimes you may want the wait to be interuptible by simply pressing a key on the keyboard. In such cases you should consider using the inkey$-function, with a number of seconds as an argument).
deg=0
do
maxx=44+40*sin(deg)
for x=1 to maxx
print "*";
next x
pause 0.1+(maxx*maxx/(4*84*84))
print
deg=deg+0.1
loop
This example draws a sine-curve; due to the pause-statement the speed of drawing varies in the same way as the speed of a ball might vary, if it would roll along this curve under the influence of gravity.
peek — retrieve various internal informations
print peek("foo")
a=peek(#1)
The peek-function has many different and mostly unrelated uses. It is a kind of grabbag for retrieving all kinds of numerical information, internal to yabasic. The meaning of the numbers returned be the peek-function depends on the string or number passed as an argument.
peek always returns a number, however the closely related peek$-function exists, which may be used to retrieve string information from among the internals of yabasic. Finally note, that some of the values which are retrieved with peek may even be changed, using the poke-function.
There are two variants of the peek-function: One expects an integer, positive number and is described within the first entry of the list below. The other variant expects one of a well defined set of strings as described in the second and all the following entries of the list below.
Read a single character from the file a (which must be open of course).
Return the height of the graphic-window in pixels. If none is open, this peek will return the height of the last window opened or 100, if none has been opened yet.
Return the width of the graphic-window in pixels. If none is open, this peek will return the width of the last window opened or 100, if none has been opened yet.
Return the height of the font used within the graphic window. If none is open, this peek will return the height of the last font used or 10, if no window has been opened yet.
Return the height in characters of the window, wherein yabasic runs. If you have not called clear screen yet, this peekwill return 0, regardless of the size of your terminal.
Return the width in characters of the window, wherein yabasic runs. If you have not called clear screen yet, this peekwill return 0, regardless of the size of your terminal.
Return the number of arguments, that have been passed to yabasic at invocation time. E.g. if yabasic has been called like this: yabasic foo.yab bar baz, then peek("argument") will return 2. This is because foo.yab is treated as the name of the program to run, whereas bar and baz are considered arguments to the program, which are passed on the commandline. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this peekwill mostly return 0.
The function peek("argument") can be written as peek("arguments") too.
You will want to check out the corresponding function peek$("argument") to actually retrieve the arguments. Note, that each call to peek$("argument") reduces the number returned by peek("argument").
Return true, if the executing yabasic-program is part of a standalone program; see the section about creating a standalone-program for details.
Return the version number of yabasic (e.g. 2.72).
Return a number specifying the nature of the last error in an open- or seek-statement. Normally an error within an open-statement immediately terminates your program with an appropriate error-message, so there is no chance and no need to learn more about the nature of the error. However, if you use open as a condition (e.g. if (open(#1,"foo")) …) the outcome (success or failure) of the open-operation will determine, if the condition evaluates to true or false. If now such an operation fails, your program will not be terminated and you might want to learn the reason for failure. This reason will be returned by peek("error") (as a number) or by peek$("error") (as a string)
The table below shows the various error codes; the value returned by peek$("error") explains the nature of the error. Note, that the codes 10,11 and 12 refer to the seek-command.
Table 6.1. Error codes
| peek("error") | peek$("error") | Explanation |
|---|---|---|
| 2 | Stream already in use | Do not try to open one and the same filenumber twice; rather close it first. |
| 3 | 'x' is not a valid filemode | The optional filemode argument, which may be passed to the open-function, has an invalid value |
| 4 | could not open 'foo' | The open-call did not work, no further explanation is available. |
| 5 | reached maximum number of open files | You have opened more files than your operating system permits. |
| 6 | cannot open printer: already printing graphics | The commands open printer and open #1,printer both open a printer (refer to their description for the difference). However, only one can be active at a time; if you try to do both at the same time, you will receive this error. |
| 7 | could not open line printer | Well, it simply did not work. |
| 9 | invalid stream number | An attempt to use an invalid (e.g. negative) stream number; example: open(-1,"foo") |
| 10 | could not position stream x to byte y | seek did not work. |
| 11 | stream x not open | You have tried to seek within a stream, that has not been opened yet. |
| 12 | seek mode 'x' is none of begin,end,here | The argument, which has been passed to seek is invalid. |
open "foo" for reading as #1
open "bar" for writing as #2
while(not eof(#1))
poke #2,chr$(peek(#1));
wend
This program will copy the file foo byte by byte to bar.
Note, that each peek does something entirely different, and only one has been demonstrated above. Therefore you need to make up examples yourself for all the other peeks.
peek$ — retrieve various internal string-informations
print peek$("foo")
The peek$-function has many different and unrelated uses. It is a kind of grabbag for retrieving all kinds of string information, internal to yabasic; the exact nature of the strings returned be the peek$-function depends on the string passed as an argument.
peek$ always returns a string, however the closely related peek-function exists, which may be used to retrieve numerical information from among the internals of yabasic. Finally note, that some of the values which are retrieved with peek$ may even be changed, using the poke-function.
The following list shows all possible arguments to peek$:
Returns either "debug", "note", "warning", "error" or "fatal", depending on the current infolevel. This value can be specified with an option (either under windows or unix) on the commandline or changed during the execution of the program with the corresponding poke; however, normally only the author of yabasic (me !) would want to change this from its default value "warning".
Returns one of nine possible strings, specifying the default alignment of text within the graphics-window. The alignment-string returned by this peek describes, how the text-command aligns its string-argument with respect to the coordinates supplied. However, this value does not apply, if the text-command explicitly specifies an alignment. Each of these strings is two characters long. The first character specifies the horizontal alignment and can be either l, r or c, which stand for left, right or center. The second character specifies the vertical alignment and can be one of t, b or c, which stand for top, bottom or center respectively.
You may change this value with the corresponding command poke "textalign",…; the initial value is lb, which means the top of the left and the top edge if the text will be aligned with the coordinates, that are specified within the text-command.
This peek returns a two character string, which specifies the position of the origin of the coordinate system of the window; this string might be changed with the corresponding command poke "windoworigin",x,y or specified as the argument of the origin command; see there for a detailed description of the string, which might be returned by this peek.
Return a string describing the nature of the last error in an open- or seek-statement. See the corresponding peek("error") for a detailed description.
Return the name of the library, this statement is contained in. See the import-command for a detailed description or for more about libraries.
This peek returns the name of the operating system, where your program executes. This can be either windows or unix.
Return the name of the font, which is used for text within the graphic window; this value can be specified as the third argument to the open window-command.
Return the environment variable specified by NAME (which may be any string expression). Which kind of environment variables are available on your system depends, as well as their meaning, on your system; however typing env on the commandline will produce a list (for Windows and Unix alike). Note, that peek$("env",...) can be written as peek$("environment",...) too.
Return one of the arguments, that have been passed to yabasic at invocation time (the next call will return the the second argument, and so on). E.g. if yabasic has been called like this: yabasic foo.yab bar baz, then the first call to peek$("argument") will return bar. This is because foo.yab is treated as the name of the program to run, whereas bar and baz are considered arguments to this program, which are passed on the commandline. The second call to peek$("argument") will return baz. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this peekwill mostly return the empty string.
Note, that peek$("argument") can be written as peek$("arguments").
Finally you will want to check out the corresponding function peek("argument").
print "You have supplied these arguments: "
while(peek("argument"))
print peek("argument"),peek$("argument")
wend
If you save this program in a file foo.yab and execute it via yabasic t.yab a b c (for windows users: please use the commandline for this), your will get this output:
3a 2b 1c
pi — a constant with the value 3.14159
print pi
pi is 3.14159265359 (well at least for yabasic); do not try to assign to pi (e.g. pi=22/7) this would not only be mathematically dubious, but would also result in a syntax error.
for a=0 to 180
print "The sine of ",a," degrees is ",sin(a*pi/180)
next a
This program uses pi to transform an angle from degrees into radians.
poke — change selected internals of yabasic
poke "foo","bar" poke "foo",baz poke #a,"bar" poke #a,baz
The poke-command may be used to change details of yabasics behaviour. Like the related function peek, poke does many different things, depending on the arguments supplied.
Here are the different things you can do with poke:
This poke changes the default alignment of text with respect to the coordinates supplied within the text-command. However, this value does not apply, if the text-command explicitly specifies an alignment. The second argument ("cc" in the example) must always be two characters long; the first character can be one of l (left), r (right) or c (center); the second character can be either t (top), b (bottom) or c (center); see the corresponding peek$("textalign") for a detailed description of this argument.
This poke moves the origin of the coordinate system of the window to the specified position. The second argument ("lt" in the example) must always be two characters long; the first character can be one of l (left), r (right) or c (center); the second character can be either t (top), b (bottom) or c (center). Together those two characters specify the new position of the coordinate-origin. See the corresponding peek$("windoworigin") for a more in depth description of this argument.
Change the amount of internal information, that yabasic outputs during execution.
The second argument can be either "debug", "note", "warning", "error" or "fatal". However, normally you will not want to change this from its default value "warning".
See also the related peek$("infolevel").
Write the given byte (a in the example above) to the specified stream (#a in the example).
See also the related function function peek(#1).
print "Hello, now you will see, how much work"
print "a simple for-loop involves ..."
input "Please press return " a$
poke "infolevel","debug"
for a=1 to 10:next a
This example only demonstrates one of the many pokes, which are described above: The program switches the infolevel to debug, which makes yabasic produce a lot of debug-messages during the subsequent for-loop.
print — Write to terminal or file
print "foo",a$,b
print "foo","a$,b;
print #a "foo",a$
print #a "foo",a$;
print foo using "##.###"
print reverse "foo"
print at(10,10) a$,b
print @(10,10) a$,b
print color("red","blue") a$,b
print color("magenta") a$,b
print color("green","yellow") at(5,5) a$,b
The print-statement outputs strings or characters, either to your terminal (also known as console) or to an open file.
To understand all those uses of the print-statement, let's go throught the various lines in the synopsis above:
Print the string foo as well as the contents of the variables a$ and b onto the screen, silently adding a newline.
(Note the trailing semicolon !) This statement does the same as the one above; only the implicit newline is skipped, which means that the next print-statement will append seamlessly.
This is the way to write to files. The file with the number a must be open already, an implicit newline is added. Note the file-number #a, which starts with a hash ('#') amd is separated from the rest of the statement by a space only. The file-number (contained in the variable a) must have been returned by a previous open-statement (e.g. a=open("bar")).
The same as above, but without the implicit newline.
Print the number foo with as many digits before and after the decimal dot as given by the number of '#'-signs. See the entries for using and str$ for a detailed description of this format.
As all the print-variants to follow, this form of the print-statement can only be issued after clear screen has been called. The strings and numbers after the reverse-clause are simply printed inverse (compared to the normal print-statement).
Print at the specified (x,y)-position. This is only allowed after clear screen has been called. You may want to query peek$("screenwidth") or peek$("screenheight") to learn the actual size of your screen. You may add a semicolon to suppress the implicit newline.
This is exactly the same as above, however, at may be written as @.
Print with the specified fore- ("red") and background ("blue") color (or colour). The possible values are "black", "white", "red", "blue", "green", "yellow", "cyan" or "magenta". Again, you need to call clear screen first and add a semicolon if you want to suppress the implicit newline.
You may specify the foreground color only.
A color and a position (in this sequence, not the other way around) may be specified at once.
clear screen
columns=peek("screenwidth")
lines=peek("screenheight")
dim col$(7)
for a=0 to 7:read col$(a):next a
data "black","white","red","blue","green","yellow","cyan","magenta"
for a=0 to 2*pi step 0.1
print colour(col$(mod(i,8))) at(columns*(0.8*sin(a)+0.9)/2,lines*(0.8*cos(a)+0.9)/2) "*"
i=i+1
next a
This example draws a cloured ellipse within the text window.
putbit — draw a rectangle of pixels into the graphic window
open window 200,200 … a$=getbit(20,20,50,50) … putbit a$,30,30 putbit a$ to 30,30 putbit a$,30,30,"or"
The putbit-command is the counterpart of the getbit-function. putbit requires a string as returned by the getbit-function. Such a string contains a rectangle from the graphic window; the putbit-function puts such a rectangular region back into the graphic-window.
Note, that the putbit-command currently accepts a third argument. However only the string value "or" is supported here. The effect is, that only those pixel, which are set in the string will be set in the graphic window. Those pixels, which are not set in the string, will not change in the window (as opposed to beeing cleared).
Note, that the format of the string returned by this function is due to change as soon as yabasic will learn, how to deal with colors.
c$="41,41:0000000000000000000000000400000000cff1000000ffff100000ffff700008fffff30008ffffff0008ffffff3008fffffff000fffffff100fffffff700ffffffff10efffffff30cfffffff70cffffffff18ffffffff30ffffffff70effffffff0cffffffff1cffffffff30ffffffff70effffffff0cffffffff18ffffffff30ffffffff70cfffffff708ffffffff00ffffffff10cfffffff100fffffff100effffff3008ffffff3000efffff30008fffff30000cffff100000ffff1000000ff700000000000000000000000000000000000"
open window 200,200
do
x=ran(200)
y=ran(200)
putbit c$,x,y,"or"
loop
This program uses a precanned string (containing the image of a circle) and draws it repeatedly into the graphic-window. The mode "or" ensures, that no pixels will be cleared.
putscreen — draw a rectangle of characters into the text terminal
clear screen … a$=getscreen$(5,5,10,10) … putscreen a$,7,7
The putscreen-command is the counterpart of the getscreen$-function. putscreen requires a string as returned by the getscreen-function. Such a string contains a rectangular detail from the terminal; the putscreen-function puts such a region back into the terminal-window.
Note, that clear screen must have been called before.
clear screen
for a=1 to 200
print color("red") "Hallo !";
print color("blue") "Welt !";
next a
r$=getscreen$(0,0,20,20)
for x=0 to 60
putscreen r$,x,0
sleep 0.1
next x
This example prints the string "Hallo !Welt !" all over the screen and then moves a rectangle from one side to the other.
Table of Contents
ran() — return a random number
print ran() x=ran(y)
The ran-function returns a random number. If no argument is given, the number returned is in the range from 0 to 1; where only 0 is a possible value; 1 will never be returned. If an argument is supplied, the number returned will be in the range from 0 up to this argument, whereas this argument itself is not a possible return value.
clear screen
c=peek("screenwidth")-1
l=peek("screenheight")
dim col$(8)
for a=0 to 7:read col$(a):next a
data "black","white","red","blue","green","yellow","cyan","magenta"
do
x=ran(c)
y=l-ran(l*exp(-32*((x/c-1/2)**2)))
i=i+1
print color(col$(mod(i,8))) at(x,y) "*";
loop
This example will print a cloured bell-curve.
read — read data from data-statements
read a$,a … data "Hello !",7
The read-statement retrieves literal data, which is stored within data-statements elsewhere in your program.
read num
dim col$(num)
for a=1 to num:read col$(a):next a
clear screen
print "These are the colours known to yabasic:\n"
for a=1 to num
print colour(col$(a)) col$(a)
next a
data 8,"black","white","red","blue"
data "green","yellow","cyan","magenta"
This program prints the names of the colors known to yabasic in those very colors.
rectangle — draw a rectangle
open window 100,100 rectangle 10,10 to 90,90 rectangle 20,20,80,80 rect 20,20,80,80 box 30,30,70,70 clear rectangle 30,30,70,70 fill rectangle 40,40,60,60 clear fill rectangle 60,60,40,40
The rectangle-command (also known as box or rect, for short) draws a recatangle; it accepts four parameters: The x- and y-coordinates of two facing cornerpoints of the rectangle. With the optional clauses clear and fill (which may appear both and in any sequence) the rectangle can be cleared and filled respectively.
open window 200,200
c=1
do
for phi=0 to pi step 0.1
if (c) then
rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
else
clear rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
endif
sleep 0.1
next phi
c=not c
loop
This example draws a nice animated pattern; watch it for a couple of hours, to see how it develops.
redim — create an array prior to its first use. A synonym for dim
See the dim-command.
The redim-command does exactly the same as the dim-command; it is just a synonym. redim has been around in older versions of basic (not even yabasic) for many years; therefore it is supported in yabasic for compatibility reasons.
Please refer to the entry for the dim-command for further information.
rem — start a comment
rem Hey, this is a comment # this is a comment too // even this print "Not a comment" # This is an error !! print "Not a comment":// But this is again a valid comment print "Not a comment" // even this. print "Not a comment" rem and this !
rem introduces a comment (like # or //), that extends up to the end of the line.
Those comments do not even need a colon (':' infront of them); they (rem, # and //) all behave alike except for #, which may only appear at the very beginning of a line; therefore the fourth example in the synopsis above (print "Not a comment" # This is an error !!) is indeed an error.
Note, that rem is an abbreviation for remark. remark however is not a valid command in yabasic.
Finally note, that a comment intoduced with '#' may have a special meaning under unix; see the entry for # for details.
#
rem comments on data structures
# are more useful than
// comments on algorithms.
rem
This program does nothing, but in a splendid and well commented way.
repeat — start a repeat-loop
repeat … until (…)
The repeat-loop executes all the statements up to the final until-keyword over and over. The loop is executed as long as the condition, which is specified with the until-clause, becomes true. By construction, the statements within the loop are executed at least once.
x=0
clear screen
print "This program will print the numbers from 1 to 10"
repeat
x=x+1
print x
print "Press any key for the next number, or 'q' to quit"
if (inkey$="q") break
until(x=10)
This program is pretty much useless, but self-explanatory.
restore — reposition the data-pointer
read a,b,c,d,e,f restore read g,h,i restore foo data 1,2,3 label foo data 4,5,6
The restore-command may be used to reset the reading of data-statements, so that the next read-statement will read data from the first data-statement.
You may specify a label with the restore-command; in that case, the next read-statement will read data starting at the given label. If the label is omitted, reading data will begin with the first data-statement within your program.
input "Which language (german/english) ? " l$
if (instr("german",l$)>0) then
restore german
else
restore english
endif
for a=1 to 3
read x,x$
print x,"=",x$
next a
label english
data 1,"one",2,"two",3,"three"
label german
data 1,"eins",2,"zwei",3,"drei"
This program asks to select one of those languages known to me (i.e. english or german) and then prints the numbers 1,2 and 3 and their textual equivalents in the chosen language.
return — return from a subroutine or a gosub
gosub foo … label foo … return sub bar(baz) … return quertz end sub
The return-statement serves two different (albeit somewhat related) purposes. The probably more important use of return is to return control from within a subroutine to the place in your program, where the subroutine has been called. If the subroutine is declared to return a value, the return-statement might be accompanied by a string or number, which constitutes the return value of the subroutine.
However, even if the subroutine should return a value, the return-statement need not carry a value; in that case the subroutine will return 0 or the empty string (depending on the type of the subroutine). Moreover, feel free to place multiple return-statements within your subroutine; it's a nice way of controlling the flow of execution.
The second (but historcially first) use of return is to return to the position, where a prior gosub has left off. In that case return may not carry a value.
do
read a$
if (a$="") then
print
end
endif
print mark$(a$)," ";
loop
data "The","quick","brown","fox","jumped"
data "over","the","lazy","dog",""
sub mark$(a$)
if (instr(lower$(a$),"q")) return upper$(a$)
return a$
end sub
This example features a subroutine mark$, that returns its argument in upper case, if it contains the letter "q", or unchanged otherwise. In the test-text the word quick will end up beeing marked as QUICK.
The example above demonstrates return within subroutines; please see gosub for an example of how to use return in this context.
reverse — print reverse (background and foreground colors exchanged)
clear screen … print reverse "foo"
reverse may be used to print text in reverse. reverse is not a seperate command, but part of the print-command; it may be included just after the print and can only be issued once that clear screen has been issued.
clear screen
print "1 ";
c=3
do
prim=true
for a=2 to sqrt(c)
if (frac(c/a)=0) then
prim=false
break
endif
next a
if (prim) then
print
print reverse c;
else
print c;
endif
print " ";
c=c+1
loop
This program prints numbers from 1 on and marks each prime number in reverse.
at, color, print, clear screen
right$() — return (or change) the right end of a string
print right$(a$,2) right$(b$,2)="baz"
The right$-function requires two arguments (a string and a number) and returns the part from the right end of the string, whose length is specified by its second argument. So, right$ simply returns the requested number of chars from the right end of the given string.
Note, that the right$-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the right$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.
print "Please enter a length either in inch or centimeter"
print "please add 'in' or 'cm' to mark the unit."
input "Length: " a$
if (right$(a$,2)="in") then
length=val(a$)*2.56
elsif (right$(a$,2)="cm") then
length=val(a$)
else
error "Invalid input: "+a$
endif
This program allows the user to enter a length qulified with a unit (either inch or centimeter).
This second example demonstrates the capability to assign to the right$-function.
a$="Heiho World !" print a$ right$(a$,7)="dwarfs." print a$
rinstr() — find the rightmost occurence of one string within the other
pos=rinstr("Thequickbrownfox","equi")
pos=rinstr(a$,b$,x)
The rinstr-function accepts two string-arguments and tries to find the second within the first. However, unlike the instr, the rinstr-function finds the rightmost (or last) occurence of the string; whereas the instr-function finds the leftmost (or first) occurence. In any case however, the position is counted from the left.
If you supply a third, numeric argument to the rinstr-function, it will be used as a starting point for the search. Therefore rinstr("abcdeabcdeabcde","e",8) will return 5, because the search for an "e" starts at position 8 and finds the first one at position 5.
print rinstr("foofoofoobar","foo")
This simple example will print 7, because it finds the rightmost among the three occurences of foo within the string. Note, that
print instr("foofoofoobar","foo")
would have printed 1.
rtrim$() — trim spaces at the right end of a string
a$=rtrim$(b$)
The rtrim$-function removes all wthitespace from the right end of a string and returns the result.
open 1,"foo"
dim lines$(100)
l=1
while(not eof(1))
input #1 a$
a$=rtrim$(a$)
if (right$(line$,1)="\\") then
line$=line$+" "+a$
else
lines$(l)=line$
l=l+1
line$=a$
endif
end while
print "Read ",l," lines"
This example reads the file foo allowing for continuation lines, which are marked by a \, which appears as the last character on a line. For convenience whitespace at the right end of a line is trimmed with rtrim.
Table of Contents
screen — as clear screen clears the text window
clear screen
The keyword screen appears only within the sequence clear screen; please see there for a description.
seek() — change the position within an open file
open 1,"foo" seek #1,q seek #1,x,"begin" seek #1,y,"end" seek #1,z,"here"
The seek-command changes the position, where the next input (or peek) statement will read from an open file. Usually files are read from the beginning to the end sequentially; however sometimes you may want to depart from this simple scheme. This can be done with the seek-command, allowing you to change the position, where the next piece of data will be read from the file.
seek accepts two or three arguments: The first one is the number of an already open file. The second one is the position where the next read from the file will start. The third argument is optional and specifies the the point from where the position (the second argument) will count. It can be one of:
Count from the beginning of the file.
Count from the end of the file.
Count from the current position within the file.
open #1,"count.dat","w"
for a=1 to 10
print #1,"00000000";
if (a<10) print #1,";";
next a
dim count(10)
do
x=int(ran(10))
i=i+1
if (mod(i,1000)=0) print ".";
count(x)=count(x)+1
curr$=right$("00000000"+str$(count(x)),8)
seek #1,9*x,"begin"
print #1,curr$;
loop
This example increments randomly one of ten counters (in the array count()); however, the result is always kept and updated within the file count.dat, so even in case of an unexpected interrupt, the result will not be lost.
sig() — return the sign of its argument
a=sig(b)
Return +1, -1 or 0, if the single argument is positive, negative or zero.
clear screen
dim c$(3):c$(1)="red":c$(2)="white":c$(3)="green"
do
num=ran(100)-50
print color(c$(2+sig(num))) num
loop
This program prints an infinite sequence of random number; positive numbers are printed in green, negative numbers are printed red (an exact zero would be printed white). (With a little extra work, this program could be easily extended into a brogerage system)
sin() — return the sine of its single argument
y=sin(angle)
The sin-function expects an angle (in radian, not degree) and returns its sine.
open window 200,200
new curve
for phi=0 to 2*pi step 0.1
line to 100+90*sin(phi),100+90*cos(phi)
next phi
close curve
This program draws a circle (ignoring the existence of the circle-command).
sleep — pause, sleep, wait for the specified number of seconds
sleep 4
The sleep-command has many different names: You may write pause, sleep or wait interchangable; whatever you write, yabasic will always do exactly the same.
Therefore you should refer to the entry for the pause-function for further information.
split() — split a string into many strings
dim w$(10) … num=split(a$,w$()) num=split(a$,w$(),s$)
The split-function requires a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).
The split-function regards its first argument (a string) as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference you have supplied. Note, that the array, which is passed as a reference (w$() in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. w$(0)) will not be used.
normally (i.e. if you omit the third, which is the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;) will delimit tokens.
Note, that a sequence of separator-characters will produce a sequence of empty tokens; that way, the number of tokens returned will always be one plus the number of separator characters contained within the string. Refer to the closely related token-function, if you do not like this behaviour. In some way, the split-function focuses on the separators (other than the token-function, which focuses on the tokens), hence its name.
The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrinked) to have room for all tokens, if necessary.
The first argument finally contains the text, that will be split into tokens. The split-function returns the number of tokens that have been found.
Please see the examples below for some hints on the exact behaviour of the split-function and how it differs from the token-function:
print "This program will help you to understand, how the"
print "split()-function exactly works and how it behaves"
print "in certain special cases."
print
print "Please enter a line containing tokens separated"
print "by either '=' or '-'"
dim t$(10)
do
print
input "Please enter a line: " l$
num=split(l$,t$(),"=-")
print num," Tokens: ";
for a=1 to num
if (t$(a)="") then
print "(EMPTY)";
else
print t$(a);
endif
if (a<num) print ",";
next a
print
loop
This program prints the following output:
Please enter a line: a 1 Tokens: a Please enter a line: 0 Tokens: Please enter a line: ab 1 Tokens: ab Please enter a line: a=b 2 Tokens: a,b Please enter a line: a- 2 Tokens: a,(EMPTY) Please enter a line: a-= 3 Tokens: a,(EMPTY),(EMPTY) Please enter a line: =a- 3 Tokens: (EMPTY),a,(EMPTY) Please enter a line: a=-b 3 Tokens: a,(EMPTY),b Please enter a line: a--b- 4 Tokens: a,(EMPTY),b,(EMPTY) Please enter a line: -a==b-c== 7 Tokens: (EMPTY),a,(EMPTY),b,c,(EMPTY),(EMPTY)
sqr() — compute the square of its argument
a=sqr(b)
The sqr-function computes the square of its numerical argument (i.e. it multiplies its argument with itself).
for a=1 to 10
print a,sqr(a),a**2
next a
As you may see from the output, sqr can be written as **2 (or ^2) too.
sqrt() — compute the square root of its argument
to be written
The sqrt-function computes the square root of its numerical argument.
for a=1 to 5
print a,sqrt(a),a**(1/2)
next a
As you may see from the output, sqrt can be written as **(1/2) (or ^(1/2)) too.
static — preserves the value of a variable between calls to a subroutine
sub foo() static a … end sub
The static keyword can be used within subroutines to mark variables as static. This has two effects: First, the variable is local to the subroutine, i.e. its value is not know outside the subroutine (this is the effect of the local keyword). Second, the static-keyword arranges things, so that the variable keeps its value between invocations of the subroutine (this is different from the local-keyword).
foo()
foo()
foo()
sub foo()
static a
local b
a=a+1
b=b+1
print a,b
end sub
This program shows the difference between static and local variables within a subroutine; it produces this output:
1 1 2 1 3 1
The output shows, that the static variable a keeps its value between subroutine calls, whereas b is initialized with the value 0 at every call to the subroutine foo.
step — specifies the increment step in a for-loop
for a=1 to 10 step 3 … next a
Specify, by which amount the loop-variable of a for-loop will be incremented at each step.
The step (as well as the lower and upper bound) are computed anew in each step; this is not common, but possible, as the example below demonstrates.
for x=1 to 1000 step y
y=x+y
print x," ",y," ";
next x
print
This program computes the fibonacci numbers between 1 and 1000.
str$() — convert a number into a string
a$=str$(a) b$=str$(x,"##.###") b$=str$(x,"###,###.##") b$=str$(x,"###,###.##","_.")
The str$-function accepts a numeric argument and returns it as a string. This conversion between number and string can be controlled with the optional third argument (the format argument). See the following table of examples to learn about valid values of this argument. Note, that those examples fall in one of two categories: C-style and basic-style; the first 4 examples in the table below are C-style, the rest of the examples are basic-style. For more information on the C-style formats, you may refer to your favorite documentation on the C programming language. The basic-style formats are much simpler, they just depict the desired output, marking digits with '#'; groups of (usually three) digits may be separated with colons (','), the decimal dot must be marked by a literal dot ('.'). Moreover these characters (colons and dot) may be replaced by other characters to satisfy the needs of non-english (e.g. german) languages; see the examples below.
Note, that for clarity, each space in the result has been replaced by the letter 'x', because it would be hard to figure out, how many spaces are produced exactly otherwise.
Table 6.2. Examples for the format argument
| Example string | Result for converting 1000*pi | Description |
|---|---|---|
| %2.5f | 3141.59265 | The '2' determines the minimum length of the output; but if needed (as in the example) the output can be longer. The '5' is the number of digits after the decimal point. |
| %12.5f | xx3141.59265 | Two spaces (which appear as 'x') are added to pad the output to the requested length of 12 characters. |
| %012.5g | 0000003141.6 | The 'g' requests, that the precision ('5') specifies the overall number of digits (before and after the decimal point). |
| %-12.5f | 3141.59265xx | The '-' requests the output to be left-centered (therefor the filling space appears at thi right). |
| #####.## | x3141.59 | Each '#' specifies a digit (either before or after the dot), the '.' specifies the position of the dot. As 1000*pi does not have enough digits, the 5 requested digits before the dot are filled up with a space (which shows up as an 'x'). |
| ##,###.## | x3,141.59 | Nearly the same as above, but the colon from the format shows up within the result. |
| ##,###.## and an addtional argument of ".," | x3.141,59 | Similar to the example above, but colon and dot are replaced with dot and colon respectivly. |
| ##,###.## and an addtional argument of "_," | x3_141,59 | Similar to the example above, but colon and dot are replaced with underscore and colon respectivly. |
| ##### | x3142 | The format string does not contain a dot, and therefore the result does not have any fractional digits. |
| ##.### | ##.### | As 1000*pi has 4 digits infront of the decimal dot and the format only specifies 2, yabasic does not know what to do; therefore it chooses just to reproduce the format string. |
do
input "Please enter a format string: " f$
a$=str$(1000*pi,f$)
for a=1 to len(a$)
if (mid$(a$,a,1)=" ") mid$(a$,a,1)="x"
next a
print a$
loop
This is the program, that has been used to get the results shown in the table above.
sub — declare a user defined subroutine
foo(2,"hello") … sub foo(bar,baz$) … return qux … end sub
The sub-keyword starts the definition of a user defined subroutine. With user defined subroutines you are able to somewhat extend yabasic with your own commands or functions. A subroutine accepts arguments (numbers or strings) and returns a number or a string (however, you are not required to assign the value returned to a variable).
The name of the subroutine follows after the keyword sub. If the name (in the synopsis: foo) ends on a '$', the subroutine should return a string (with the return-statement), otherwise a number.
After the name of the subroutine yabasic requires a pair of braces; within those braces you may specify a list of parameters, for which values can (but need not) be included when calling the subroutine. If you omit one of those parameters when calling such a subroutine, it assumes the value zero (for numeric parameters) or the empty string (for string-parameters). However with peek("argument") you may find out, how many arguments have really been passed while calling the subroutine.
Parameters of a subroutine are always local variables (see the keyword local for more explanation).
From within the subroutine you may return any time with the keyword return; along with the return-keyword you may specify the return value. Note that more than one return is allowed within a single subroutine.
Finally, the keyword end sub ends the subroutine definition. Note, that the definition of a subroutine need not appear within the program before the first call to this sub.
As braces have two uses in yabasic (i.e. for supplying arguments to a subroutine as well as to list the indices of an array). yabasic can not tell apart an array from a subroutine with the same name. Therefore you cannot define a subroutine with the same name as an array !
p=2
do
if (is_prime(p)) print p
p=p+1
loop
sub is_prime(a)
local b
for b=2 to sqrt(a)
if (frac(a/b)=0) return false
next b
return true
end sub
This example is not the recommended way to compute prime numbers. However it gives a nice demonstration of using a subroutine.
switch — select one of many alternatives depending on a value
switch a case 1 case 2 … end switch … switch a$ case "a" case "b" end switch
The switch-statment selects one of many codepaths depending on a numerical or string expression. I.e. it takes an expression (either numeric or string) and compares it with a series of values, each wrapped within a case-clause. If the expression equals the value given in a case-clause, the subsequent statements are executed.
The default-clause allows to specify commands, which should be executed, if none of case-clauses matches.
Note, that many case-clauses might be clustered (e.g. case "a":case "b":case "c"). Or put another way: You need a break-statement at the end of a case-branch, if you do not want to run into the next case.
input "Please enter a single digit: " n
switch n
case 0:print "zero":break
case 1:print "one":break
case 2:print "two":break
case 3:print "three":break
case 4:print "four":break
case 5:case 6: case 7:case 8:case 9
print "Much !":break
default:print "Hey ! That was more than a single digit !"
end switch
This example translates a single digit into a string; note, how the cases 5 to 7 are clustered.
system$() — hand a statement over to your operating system and return its output
print system$("dir")
The system$-command accepts a single string argument, specifying a command, that can be found and executed by your operating system. It returns the output of this command as one big string.
input "Please enter the name of a directory: " d$
print
print "This is the contents of the '"+d$+"':"
print system$("dir "+d$)
This example lists the contents of a directory, employing the dir-command (which is about the only program, that is known under Unix as well as Windows).
system() — hand a statement over to your operating system and return its exitcode
ret=system("foo")
system("bar")
The system-command accepts a single string argument, which specifies a command to be executed. The function will return the exitcode of the command; its output (if any) will be lost.
print "Please enter the name of the file, that should be deleted."
input f$
if (system("rm "+f$+" >/dev/null 2>&1")) then
print "Error !"
else
print "okay."
endif
This program is Unix-specific: It uses the Unix-command rm to remove a file.
Table of Contents
tan() — return the tangens of its argument
foo=tan(bar)
The tan-function computes the tangens of its arguments (which should be specified in radian).
for a=0 to 45
print tan(a*pi/180)
next a
This example simply prints the tangens of all angles between 0 and 45 degree.
tell — get the current position within an open file
open #1,"foo" … position=tell(#1)
The tell-function requires the number of an open file as an argument. It returns the position (counted in bytes, starting from the beginning of the file) where the next read will start.
open #1,"foo","w"
print #1 "Hello World !"
close #1
open #1,"foo"
seek #1,0,"end"
print tell(#1)
close 1
This example (mis)uses tell to get the size of the file. The seek positions the file pointer at the end of the file, therefor the call to tell returns the total length of the file.
text — write text into your graphic-window
text x,y,"foo" text x,y,"foo","l"
The text-function displays a text-string (the third argument) at the given position (the first two arguments) within an already opened window. There is no way to specify a font for the text, that will be written (this font can only be specified once, as an argument to the open window-statement).
The fourth, optional argument can be used to specify the alignment of the text with respect to the specified position. This argument is always two characters long: The first character specifies the horizontal alignment and can be either l, r or c, which stand for left, right or center. The second character specifies the vertical alignment and can be one of t, b or c, which stand for top, bottom or center respectively. If you omit this alignment argument, the default "lb" applies; however this default may be changed with poke "textalign","xx"
open window 500,200
clear screen
data "lt","lc","lb","ct","cc","cb","rt","rc","rb"
for a=1 to 9
read align$
print "Alignment: ",align$
line 50*a-15,100,50*a+15,100
line 50*a,85,50*a,115
text 50*a,100,"Test",align$
inkey$
next a
This program draws nine crosses and writes the same text at each; however it goes through all possible nine alignment strings, showing their effect.
then — tell the long from the short form of the if-statement
if (a<b) then … endif
The keyword then is part of the if-statement; please see there for further explanations. However, not every if-statement requires the keyword then: If the keyword then is present, the if-clause may extend over more than one line, and the keyword endif is required to end it. If the keyword then is not present, the if-statement extends up to the end of the line, and any endif would be an error.
if (1<2) then
print "Hello ";
endif
if (2<3) print "world"
if (2<1)
print "!"
This example prints Hello world. Note, that no exclamation mark (!) is printed, which might come as a surprise and may be changed in future versions of yabasic.
time$ — return a string containing the current time
print time$ print time$()
The time$ function returns the current time in four fields separated by hyphens '-'. The fields are:
The current hour in the range from 0 to 23, padded with zeroes (e.g. 00 or 04) to a length of two characters.
The number of minutes, padded with zeroes.
The number of seconds, padded with zeroes.
The number of seconds, that have elapsed since the program has been started. This value encreases as long as your program runs and is therefore unbound and not padded with zeroes.
At the time of writing this documentation, time$ returns 22-58-53-0. Note, that the first three of the four fields returned by time$ have a fixed width; therefore it is easy to extract some fields with the usual string-functions mid$ (and others).
print "Hello it is ",time$
print "An empty for-loop with ten million iterations takes ";
s=val(mid$(time$,10))
for a=1 to 10000000:next a
e=val(mid$(time$,10))
print e-s," seconds"
This program benchmarks the for-loop and uses the fourth field of the string returned by time$.
to — this keyword appears as part of other statements
for a=1 to 100 step 2 … next a line x,y to a,b
The to-keyword serves two purposes (which are not related at all):
within for-statements, to specify the upper bound of the loop.
Within any graphical command (e.g. line), that requires two points (i.e. four numbers) as arguments, a comma ',' might be replaced with the keyword to. I.e. instead of 100,100,200,200 you may write 100,100 to 200,200 in such commands.
Pleas see the command listed under "See also" for examples.
token() — split a string into multiple strings
dim w$(10) … num=token(a$,w$()) num=token(a$,w$(),s$)
The token-function accepts a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).
The token-function regards its first argument as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference that has been supplied. Note, that the array, which is passed as a reference (w$() in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. w$(0)) will not be used.
Normally (i.e. if you omit the third, the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;) will delimit tokens.
Note, that token will never produce empty tokens, even if two or more separators follow in sequence. Refer to the closely related split-function, if you do not like this behaviour. In some way, the token-function focuses on the tokens and not on the separators (other than the split-function, which focuses on the separators).
The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrinked) as necessary to have room for all tokens.
The first argument finally contains the text, that will be split into tokens. The token-function returns the number of tokens, that have been found.
Please see the examples below for some hints on the exact behaviour of the token-function and how it differs from the split-function:
print "This program will help you to understand, how the"
print "token()-function exactly works and how it behaves"
print "in certain special cases."
print
print "Please enter a line containing tokens separated"
print "by either '=' or '-'"
dim t$(10)
do
print
input "Please enter a line: " l$
num=token(l$,t$(),"=-")
print num," Tokens: ";
for a=1 to num
if (t$(a)="") then
print "(EMPTY)";
else
print t$(a);
endif
if (a<num) print ",";
next a
print
loop
This program prints the following output:
Please enter a line: a 1 Tokens: a Please enter a line: 0 Tokens: Please enter a line: ab 1 Tokens: ab Please enter a line: a=b 2 Tokens: a,b Please enter a line: a- 1 Tokens: a Please enter a line: a-= 1 Tokens: a Please enter a line: =a- 1 Tokens: a Please enter a line: a=-b 2 Tokens: a,b Please enter a line: a--b- 2 Tokens: a,b Please enter a line: -a==b-c== 3 Tokens: a,b,c
trim$() — remove leading and trailing spaces from its argument
a$=trim$(b$)
The trim$-function removes all whitespaces from the left and from the right end of a string and returns the result. Calling trim$ is equivalent to calling rtrim$(ltrim$()).
do
input "Continue ? Please answer yes or no: " a$
a$=lower$(trim$(a$))
if (len(a$)>0 and a$=left$("no",len(a$)) exit
loop
This example asks for an answer (yes or no) and removes spaces with trim$ to make the comparison with the string "no" more bulletproof.
true — a constant with the value of 1
okay=true
The constant true can be assigned to variables which will later appear in conditions (e.g. an if-statement.
true may also be written as TRUE or even TrUe.
input "Please enter a string of all upper letters: " a$
if (is_upper(a$)) print "Okay"
sub is_upper(a$)
if (a$=upper$(a$)) return true
return false
end sub
Table of Contents
until — end a repeat-loop
repeat … until (…)
The until-keyword ends a loop, which has been introduced by the repeat-keyword. until requires a condition in braces (or an expression, see here for details) as an argument; the loop will continue until this condition evaluates to true.
c=1
s=1
repeat
l=c
s=-(s+sig(s))
c=c+1/s
print c
until(abs(l-c)<0.000001)
This program calculates the sequence 1/1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+ … ; please let me know, if you know against which value this converges.
upper$() — convert a string to upper case
u$=upper$(a$)
The upper$-function accepts a single string argument and converts it to all upper case.
line input "Please enter a sentence without the letter 'e': " l$
p=instr(upper$(l$),"E")
if (p) then
l$=lower$(l$)
mid$(l$,p,1)="E"
print "Hey, you are wrong, see here!"
print l$
else
print "Thanks."
endif
This program asks for a sentence and marks the first (if any) occurence of the letter 'e' by coverting it to upper case (in contrast to the rest of the sentence, which is converted to lower case).
using — Specify the format for printing a number
print a using "##.###"
print a using("##.###",",.")
The using-keyword may appear as part of the print-statement and specifies the format (e.g. the number of digits before and after the decimal dot), which should be used to print the number.
The possible values for the format argument ("##.###" in the synopsis above) are described within the entry for the str$-function; especially the second line in the synopsis (print a using("##.###",",.")) will become clear after referring to str$. In fact the using clause is closely related to the str$-function; the former can always be rewritten using the latter; i.e. print foo using bar$ is always equivalent to print str$(foo,bar$). Therefore you should check out str$ to learn more.
for a=1 to 10
print sqrt(ran(10000*a)) using "#########.#####"
next a
This example prints a column of square roots of random number, nicely aligned at the decimal dot.
Table of Contents
val() — converts a string to a number
x=val(x$)
The val-function checks, if the start of its string argument forms a floating point number and then returns this number. The string therefore has to start with digits (only whitespace infront is allowed), otherwise the val-function returns zero.
input "Please enter a length, either in inches (in) or centimeters (cm) " l$
if (right$(l$,2)="in") then
l=val(l$)*2.51
else
l=val(l$)
print "You have entered ",l,"cm."
This example queries for a length and checks, if it has been specified in inches or centimeters. The length is then converted to centimeters.
Table of Contents
wait — pause, sleep, wait for the specified number of seconds
wait 4
The wait-command has many different names: You may write pause, sleep or wait interchangeable; whatever you write, yabasic will always do exactly the same.
Therefore you should refer to the entry for the pause-function for further information.
wend — end a while-loop
while(a<b) … wend
The wend-keyword marks the end of a while-loop. Please see the while-keyword for more details.
wend can be written as end while or even end-while.
line input "Please enter a sentence: " a$
p=instr(a$,"e")
while(p)
mid$(a$,p,1)="E"
p=instr(a$,"e")
wend
print a$
This example reads a sentence and converts every occurence of the letter e into uppercase (E).
while (which is just the following entry).
while — start a while-loop
while(…) … wend
The while-keyword starts a while-loop, i.e. a loop that is excuted as long as the condition (which is specified in braces after the keyword while) evaluates to true.
Note, that the body of such a while-loop will not be executed at all, if the condition following the while-keyword is not true initially.
If you want to leave the loop prematurely, you may use the break-statement.
open #1,"foo"
while(!eof(1))
line input #1 a$
print a$
wend
This program reads the file foo and prints it line by line.
origin — move the origin of a window
open window 200,200 origin "cc"
The origin-command applies to graphic windows and moves the origin of the coordinate system to one of nine point within the window. The normal position of the origin is in the upper left corner of the window; however in some cases this is inconvenient and moving the origin may save you from substracting a constant offset from all of your coordinates.
However, you may not move the origin to an arbitrary position; in horizontal possition there are only three positions: left, center and right, which are decoded by the letters l, c and r. In vertical position the allowed positions are top, center and bottom; encoded by the letters t, c and b. Taking the letters together, you arrive at a string, which might be passed as an argument to the command; e.g. "cc" or "rt".
open window 200,200
window origin "cc"
circle 0,0,60
This example draws a circle, centered at the center of the window.
Table of Contents
xor() — compute the exclusive or
x=xor(a,b)
The xor computes the bitwise exclusive or of its two numeric arguments. To understand the result, both arguments should be viewed as binary numbers (i.e. a series of 0 and 1); a bit of the result will then be 1, if exactly one argument has a 1 and the other has a 0 at this position in their binary representation.
Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to and.
print xor(7,4)
This will print 3. This result is obvious, if you note, that the binary representation of 7 and 4 are 111 and 100 respectively; this will yield 011 in binary representaion or 2 as decimal.
The eor-function is the same as the xor function; both are synonymous; however they have each their own description, so you may check out the entry of eor for a slightly different view.
Table of Contents
# — either a comment or a marker for a file-number
# This is a comment, but the line below not ! open #1,"foo"
The hash ('#') has two totally unrelated uses:
A hash might appear in commands related with file-io. yabasic uses simple numbers to refer to open files (within input, print, peek or eof). In those commands the hash may precede the number, which species the file. Please see those commands for further information and examples; the rest of this entry is about the second use (as a comment).
As the very first character within a line, a hash introduces comments (similar to rem).
'#' as a comment is common in most scripting languages and has a special use under Unix: If the very first line of any Unix-program begins with the character sequence '#!' ("she-bang", no spaces allowed), the rest of the line is taken as the program that should be used to execute the script. I.e. if your yabasic-program starts with '#!/usr/local/bin/yabasic', the program /usr/local/bin/yabasic will be invoked to execute the rest of the program. As a remark for windows-users: This mechanism ensures, that yabasic will be invoked to execute your program; the ending of the file (e.g. .yab) will be ignored by Unix.
# This line is a valid comment
print "Hello " : # But this is a syntax error, because
print "World!" : # the hash is not the first character !
Note, that this example will produce a syntax error and is not a valid program !
// — starts a comment
// This is a comment !
The double-slash ('//') is (besides REM and '#') the third way to start a comment. '//' is the latest and greatest in the field of commenting and allows yabasic to catch up with such cool languages like C++ and Java.
// Another comment.
print "Hello world !" // Another comment
Unlike the example given for '#' this example is syntactically correct and will not produce an error.
@ — synonymous to at
clear screen … print @(a,b)
As '@' is simply a synonym for at, please see at for further information.
: — separate commands from each other
print "Hello ":print "World"
The colon (':') separates multiple commands on a single line.
The colon and the newline-character have mostly the same effect, only that the latter, well, starts a new line too. The only other difference is their effect within the (so-called) short if, which is an if-statement without the keyword then. Please see the entry for if for more details.
if (a<10) print "Hello ":print "World !"
This example demonstrates the difference between colon and newline as described above.
; — suppress the implicit newline after a print-statement
print "foo",bar;
The semicolon (';') may only appear at the last position within a print-statement. It supresses the implicit newline, which yabasic normally adds after each print-statement.
Put another way: Normally the output of each print-statement appears on a line by itself. If you rather want the output of many print-statements to appear on a single line, you should end the print-statement with a semicolon.
print "Hello ";:print "World !"
This example prints Hello World ! in a single line.
** or ^ — raise its first argument to the power of its second
print 2**b print 3^4
** (or ^, which is an exact synonym), is the arithmetic operator of exponentiation; it requires one number to its left and a second one to its right; ** then raises the first argument to the power of the second and returns the result. The result will only be computed if it yields a real number (as opposed to a complex number); this means, that the power can not be computed, if the first argument is negative and the second one is fractional. On the other hand, the second argument can be fractional, if the first one ist positive; this means, that ** may be used to compute arbitrary roots: e.g. x**0.5 computes the square root of x.
print 2**0.5
Table of Contents
This chapter presents some general concepts and terms, which deserve a description on their own, but are not associated with a single command or function in yabasic. Most of these topics do not lend themselves to be read alone, rather they might be read (or skimmed) as background material if an entry from the alphabetical list of commands refers to them.
Logical shortcuts are no special language construct and there is no keyword for them; they are just a way to evaluate logical expressions. Logical expressions (i.e. a series of conditions or comparisons joined by and or or) are only evaluated until the final result of the expression can be determined. An example:
if (a<>0 and b/a>2) print "b is at least twice as big as a"
The logical expression a<>0 and b/a>2 consists of two comparisons, both of which must be true, if the print statement should be executed. Now, if the first comparison (a<>0) is false, the whole logical expression can never be true and the second comparison (b/a>2) need not be evaluated.
This is exactly, how yabasic behaves: The evaluation of a composed logical expressions is terminated immediately, as soon as the final result can be deduced from the already evaluated parts.
In practice, this has the following consequences:
If two or more comparisons are joined with and and one comparison results in false, the logical expression is evaluated no further and the overall result is false.
If two or more comparisons are joined with or and one comparison results in true, the logical expression is evaluated no further and the result is true.
“Nice, but whats this good for ?”, I hear you say. Well, just have another look at the example, especially the second comparison (b/a>2); deviding b by a is potentially hazardous: If a equals zero, the expression will cause an error and your program will terminate. To avoid this, the first part of the comparison (a<>0) checks, if the second one can be evaluated without risk. This pre-checking is the most common usage and primary motivation for logical shortcuts (and the reason why most programming languages implement them).
Well, bottomline there is no difference or distinction between conditions and expressions, at least as yabasic is concerned. So you may assign the result of comparisons to variables or use an arithmetic expression or a simple variable within a condition (e.g. within an if-statement). So the constructs shown in the example below are all totally valid:
input "Please enter a number between 1 and 10: " a rem Assigning the result of a comparison to a variable okay=a>=1 and a<=10 rem Use a variable within an if-statement if (not okay) error "Wrong, wrong !"
So conditions and expressions are really the same thing (at least as long as yabasic is concerned). Therefore the terms conditions and expression can really be used interchangeably, at least in theory. In reality the term condition is used in connection with if or while whereas the term expression tends to be used more often within arithmetic context.
References on arrays are the only way to refer to an array as a whole and to pass it to subroutines or functions like arraydim or arraysize. Whereas (for example) a(2) designates the second element of the array a, a() (with empty braces) refers to the array a itself. a() is called an array reference.
If you pass an array reference to one of your own subroutines, you need to be aware, that the subroutine will be able to modify the array you have passed in. So passing an array reference does not create a copy of the array; this has some interesting consequences:
Speed and space: Creating a copy of an array would be a time- and resourceconsuming operation; passing just a reference is cheap and fast.
Returning many values: A subroutine, that wants to give back more than one value, may require an array reference among its arguments and then store its many return values within this array. This is the only way to return more than one value from a subroutine.
As you probably know, windows uses the character '\' to separate the directories within a pathname; an example would be C:\yabasic\yabasic.exe (the usual location of the yabasic executable). However, the very same character '\' is used to contstruct escape sequences, not only in yabasic but in most other programming languages.
Therefore the string "C:\t.dat" does not specify the file t.dat within the directory C:; this is because the sequence '\t' is translated into the tab-character. To specify this filename, you need to use the string "C:\\t.dat" (note the double slash '\\').
Escape-sequences are the preferred way of specifying 'special' characters. They ar intoduced by the '\'-character and followed by one of a few regular letters, e.g. '\n' or '\r' (see the table below).
Escape-sequences may occur within any string at any position; they are replaced at parsetime (opposed to runtime), i.e. as soon as yabasic discovers the string, with their corresponding special character. As a consequence of this len("\a") returns 1, because yabasic replaces "\a" with the matching special character just before the program executes.
Table 7.1. Escape sequences
| Escape Seqence | Matching special character |
|---|---|
| \n | newline |
| \t | tabulator |
| \v | vertical tabulator |
| \b | backspace |
| \r | carriage return |
| \f | formfeed |
| \a | alert (i.e. a beeping sound) |
| \\ | backslash |
| \' | single quote |
| \" | double quote |
| \xHEX | chr$(HEX) (see below) |
Note, that an escape sequences of the form \xHEX allows to encode arbitrary characters as long as you know their position (as a hex-number) within the ascii-charset: For example \x012 is transformed into the character chr$(18) (or chr$(dec("12",16)). Note that \x requires a hexa-decimal number (and the hexa-decimal string "12" corresponds to the decimal number 18).
The bind-feature, which is described below, is at an experimental stage right now. It works (at least for me !) under Windows and Linux, but I cannot even promise it for other variants of Unix. However, if it does not work for your Unix, I will at least try to make it work, if you give me sufficient information of your system.
Sometimes you may want to give one of your yabasic-programs to other people. However, what if those other people do not have yabasic installed ? In that case you may create a standalone-program from your yabasic-program, i.e. an executable, that may be executed on its own, standalone, even (and especially !) on computers, that do not have yabasic installed. Having created a standalone program, you may pass it around like any other program (e.g. one written in C) and you can be sure that your program will execute right away.
Such a standalone-program is simply created by copying the full yabasic-interpreter and your yabasic-program (plus all the libraries it does import) together into a single, new program, whose name might be chosen at will (under windows of course it should have the ending .exe). If you decide to create a standalone-program, there are three bits in yabasic, that you may use:
The bind-command, which does the actual job of creating the standalone program from the yabasic-interpreter and your program.
The command-line Option -bind (available under windows and Unix), which does the same from the command-line.
The special peek("isbound"), which may be used to check, if the yabasic-program containing this peek is bound to the interpreter as part of a standalone program.
With these bits you know enough to create a standalone-program. Actually there are two ways to do this: on the commandline and from within your program.
Let's say you have the following very simple program within the file foo.yab:
print "Hello World !"
Normally you would start this yabasic-program by typing yabasic foo.yab and as a result the string Hello World ! would appear on your screen. However, to create a standalone-program from foo.yab you would type:
yabasic -bind foo.exe foo.yab
This command does not execute your program foo.yab but rather create a standalone-program foo.exe. Note: under Unix you would probably name the standalone program foo or such, omitting the windows-specific ending .exe.
Yabasic will confirm by printing something like: ---Info: Successfully bound 'yabasic' and 'foo.yab' into 'foo.exe'.
After that you will find a program foo.exe (which must be made executable with the chmod-command under Unix first). Now, executing this program foo.exe (or foo under Unix) will produce the output Hello World !.
This newly created program foo.exe might be passed around to anyone, even if he does not have yabasic installed.
It is possible to write a yabasic-program, that binds itself to the yabasic-interpreter. Here is an example:
if (!peek("isbound")) then
bind "foo"
print "Successfully created the standalone executable 'foo' !"
exit
endif
print "Hello World !"
If you run this program (which may be saved in the file foo.yab) via yabasic foo.yab, the peek("isbound") in the first line will check, if the program is already part of a standalone-program. If not (i.e. if the yabasic-interpreter and the yabasic-program are seperate files) the bind-command will create a standalone program foo containing both. As a result you would see the output Successfully created the standalone executable 'foo' !. Note: Under Windows you would probably choose the filename foo.exe.
Now, if you run this standalone executable foo (or foo.exe), the very same yabasic-program that is shown above will be executed again. However, this time the peek("isbound") will return TRUE and therefore the condition of the if-statement is false and the three lines after then are not executed. Rather the last print-statement will run, and you will see the output Hello World !.
That way a yabasic-program may turn itself into a standalone-program.
Now, before you go out and turn all your yabasic-programs into standalone programs, please take a second to consider the downsides of doing so:
The new standalone program will be at least as big as the interpreter itself, so you need to pass a few hundred kilobytes around, just to save people from having to install yabasic themselves.
There is no easy way to extract your yabasic-program from within the standalone program: If you ever want to change it, you need to have it around seperately.
If a new version of yabasic becomes available, again you need to recreate all of your standalone programs to take advantage of bugfixes and improvements.
So, beeing able to create a standalone program is certainly a good thin, but certainly not a silver bullet.
Table of Contents
The program below is a very simple program:
repeat input "Please enter the first number, to add " a input "Please enter the second number, to add " b print a+b until(a=0 and b=0)
This program requests two numbers, which it than adds. The process is repeated until you enter zero (or nothing) twice.
The listing below is an abbreviated and slightly refreshed version of the demo of yabasic. However this demo has been written before some of the more advanced features of yabasic have been implemented. For example subroutines have only been retrofitted on the original version of this demo. So please do not take this as a particular good example of yabasic-code. On the other hand: This is no beauty contest. However you could make it one, if you send me some better code (which should do nice and simple things with less than 200 lines).
//
// This program demoes yabasic
//
// Check, if screen is large enough
clear screen
sw=peek("screenwidth"):sh=peek("screenheight")
if (sw<78 or sh<24) then
print
print " Sorry, but your screen is to small to run this demo !"
print
end
endif
sw=78:sh=24
// Initialize everything
restore mmdata
read mmnum:dim mmtext$(mmnum)
for a=1 to mmnum:read mmtext$(a):next a
// Main loop selection of demo
ysel=1
label mainloop
clear screen
print colour("cyan","magenta") at(7,2) "################################"
print colour("cyan","magenta") at(7,3) "################################"
print colour("cyan","magenta") at(7,4) "################################"
print colour("yellow","blue") at(8,3) " This is the demo for yabasic "
yoff=7
for a=1 to mmnum
if (a=mmnum) then ydisp=1:else ydisp=0:fi
if (a=ysel) then
print colour("blue","green") at(5,yoff+ydisp+a) mmtext$(a);
else
print at(5,yoff+ydisp+a) mmtext$(a);
endif
next a
print at(3,sh-3) "Move selection with CURSOR KEYS (or u and d),"
print at(3,sh-2) "Press RETURN or SPACE to choose, ESC to quit."
do // loop for keys pressed
rev=1
do // loop for blinking
k$=inkey$(0.4)
if (k$="") then
if (ysel=mmnum) then
if (rev=1) then
print colour("blue","green") at(5,yoff+mmnum+1) mmtext$(mmnum);
rev=0
else
print colour("yellow","red") at(5,yoff+mmnum+1) mmtext$(mmnum);
rev=1
endif
endif
else // key has been pressed, leave loop
break
endif
loop // loop for blinking
yalt=ysel
if (k$="up" or k$="u") then
if (ysel=1) then ysel=mmnum else ysel=ysel-1 fi
redraw():heal():continue
fi
if (k$="down" or k$="d") then
if (ysel=mmnum) then ysel=1 else ysel=ysel+1 fi
redraw():heal():continue
fi
if (k$=" " or k$="enter" or k$="right") then
on ysel gosub overview,bitmap,endit,notyet
goto mainloop
fi
if (k$="esc") then
endit()
fi
beep
print at(3,sh-5) "Invalid key: ",k$," "
loop // loop for keys pressed
// redraw line
sub redraw()
if (yalt=mmnum) then ydisp=1:else ydisp=0:fi
print at(5,yoff+yalt+ydisp) mmtext$(yalt);
if (ysel=mmnum) then ydisp=1:else ydisp=0:fi
print colour("blue","green") at(5,yoff+ysel+ydisp) mmtext$(ysel);
return
end sub
// erase a line
sub heal()
print at(3,sh-5) " "
return
end sub
// Go here to exit
label endit
print at(3,sh-8) "Hope you liked it ...\n ";
exit
return
// Present a short overview
label overview
clear screen
print "\n Yabasic is a quite traditional basic: It comes with"
print " print, input, for-next-loops, goto, gosub, while and"
print " repeat and even user defined procedures and libraries."
print "\n Yabasic has the usual functions, from sin(), int() to mid$();"
print " more advanced functions are date$ (is ",date$,"),"
print " or token$(), system$(), ran() and glob$()."
print "\n Yabasic makes it easy to open a window, draw lines"
print " and print the resulting picture."
print "\n Yabasic programs are interpreted and run under Unix"
print " and Windows. Yabasic is small (around 200k) and"
print " free, i.e. subject to the GNU copyleft."
print "\n Finally, this demo itself is written in yabasic and"
print " gives an idea of what can be done with the language."
print "\n\n\n While you read this, I am calculating prime numbers,"
print " Press any key to return to main menu ..."
can=1
print at(6,19) "This is a prime number: "
label nextcan
can=can+2
for i=2 to sqrt(can):if (frac(can/i)=0) then goto notprime:fi:next i
print at(32,19) can;
label notprime
if (lower$(inkey$(0))<>"") then return:fi
goto nextcan
// Show some animated bitmaps
label bitmap
clear screen
print at(5,5) "Yabasic offers limited support for bitmapped graphics."
print at(5,6) "You can retrieve and alter rectangular regions of"
print at(5,7) "the graphics window with a single command."
print reverse at(5,12) " Press any key to return to main menu ... "
n=20
open window 400,400
if (picsinitialized=0) then
picsinitialized=1
dim pics(n,4)
dim pics$(5)
restore pics
for a=1 to 5:read pics$(a):next a
endif
tick=1
for a=1 to n:pics(a,4)=0:next a
cx=ran(370):cy=ran(370):vx=10-ran(20):vy=10-ran(20)
label picloop
for a=1 to n
if (pics(a,4)<=tick) then
if (pics(a,4)=tick) then
bitblit pics$(pics(a,3)) to pics(a,1),pics(a,2),"xor"
endif
x=cx+50-ran(100):y=cy+50-ran(100)
if (ran(10)>3) then
pics(a,1)=x:pics(a,2)=y:pics(a,3)=ran(5)+1
pics(a,4)=tick+4+int(ran(4))
bitblit pics$(pics(a,3)) to pics(a,1),pics(a,2),"xor"
endif
endif
next a
tick=tick+1
cx=cx+vx:cy=cy+vy
if (cx<-30 or cx>400) then cx=cx-vx:vx=-vx fi
if (cy<-30 or cy>400) then cy=cy-vy:vy=-vy fi
if (inkey$(0.1)="") then goto picloop fi
close window
return
// data for bitmaps
label pics
data "24,24:00000000000000000000000008f1000eff000fff308f9f30cf0c70e30870e30070e00070e07070e07870e0fc70e1ff30e1ff3ec1cf1ec3000fc700cf8f3cf78ffff30efff000ff00"
data "24,24:00c10000e10000f10000f10008f30008f30008f700fff700ffff30ffffffefffffefffff0ffff70eff700eff000cff100eff300fff70cfff70ef7ef1ef1cf3e700e3e100c3000000"
data "24,24:0000000000700e00700e00700e00700e10700e38700c38700c7c30087c3000fe1000ff1000ef0000e70000c70000c30000c30000e10000f10000f0000c70000c70000c3000000000"
data "24,24:000000000000008700008f30008f7000cf7000c37000e97000f97000f83008f8300878300cf8300ef8300efb300eef700fcf700f0f708700f0c700f1c300e1c100e1000000000000"
data "24,24:0000000000000cf1000cff000cff300cbf300c3c700838700c30700cff700cff700cff700c9f700c1c700e10700e10700f38708fff708fff7083ff10000000000000000000000000"
// Go here for a feature not yet implemented
label notyet
clear screen
print "\n\n Sorry this section is not yet implemented !"
print " Press any key to return to main menu ..."
inkey$
return
// Data section ...
label mmdata
// Data for main menu: Number and text of entries in main menu
data 3
data " Yabasic in a nutshell "
data " Animated Bitmaps "
data " Exit this demo "
yabasic may be copied only under the terms of the Artistic License or the GNU General Public License (GPL), both of which are distributed with yabasic.
[Can't you make up your mind ?!], I hear you say. Umm, well yes. In fact I do not want to read or try to understand them both, so I have put the burden on you (grin). However, I think that the Artistic License is more liberal and gives you more rights and you should choose it; on the other hand the GPL is more widely known and a lot of software is distributed under its terms.
Here is a list of things that are possible under the terms of the Artistic License:
Put yabasic on your own homepage or CD and even charge for the service of distributing yabasic.
Write your own yabasic-programs, pack your program and yabasic into a package and sell the whole thing.
Modify yabasic and add or remove features, sell the modified version.