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GBIC >> QBasic >> Tutorial >> Mini-Tutorial

QBasic Mini-Tutorial
Speakers know the advice of "Tell them what you're going to tell them ...", which is what this very short mini-tutorial does. It's a preview of the full tutorial provided at this site, with all the fat (and some of the meat) cut out. There's no discussion - just notes and comments.

It's an introduction for newbies to get a sense of QBasic in one reading, although some sections may not make much sense until you've read the corresponding tutorial. And for those of you coming back to QBasic after an absence, it's a reminder of what QBasic offers and perhaps what you forgot.

A Simple Program
Just to get you started, here's a quick look at a traditional "Hello World" program.

   msg$="Hello World"    # assigns a string value to the variable msg$
   print msg$            # prints value of the variable msg$ to the screen

Executing a QBasic Program
You can run a QBasic program in two ways.

  • Method 1:
    From a command line, with a QBasic program saved in a file "myprogram.bas", type in:

        qbasic /run myprogram.bas
    

    This loads the program into QBasic and then automatically runs the program. Any filename can be used but .bas is assumed if no extension is given.

  • Method 2:
    With the program loaded into the QBasic editor, simply press F5 to run the program.

Syntax

     statements end at end of line           print "hi"                 
     multiple statements per line            print "hi" : print "bye"   
     comments                                REM  line starts with REM
     comments                                'right of apostrophe
     double quotes only (no single quotes)   "yes" but not 'no'
     procedure parentheses optional          print("Hello") : print "Hello";
     

Operators

     Arithmetic             standard           +  -  *  /  =
                            integer division   \  
                            exponentiation     ^
     Numeric Compare        =   !=   <    >    <=   >=   <=>
     Boolean                and  or   not   xor  eqv  imp
                            false = 0
                            true = non-zero
     

Declarations

     dim, redim, const                       # declaration
     defint, defdbl, defsng, defstr, deflng  # declared by letter
     static, shared                          # scope
     type                                    # user-defined type
     data, read, restore                     # numeric resources
     

Variables

     declaration not required
     declaration                      Dim x$, y as Long
     variable type suffixes           single   x!       integer  x%      
                                      double   x#       long     x&
                                                        string   x$
     arrays zero-based by default     Dim x$(5), y$(3 to 5)
                                      x$(1) = "test"
     

Variable Scope

     variable scope      - limited to where declared
                         - scope is global with SHARED
     procedure variables - local to procedure
                         - STATIC stores values between calls
     

Subroutines

     Declaration required - Declare MySub (a$, b%)
                            Declare MyFunction$ (a$, b%)
     Argument list:   a as long, b as integer, c as ANY
                     
     Function  MyFunction$ (arg1, arg2, ... argn)
        ...
     End Function

     Sub  MySub (arg1, arg2, ... argn)
        ...
     End Sub

     passed variables - procedure changes have global affect
                      - enclose in () to prevent change
     
     calling procedures  -  call MySub(a$,b$)   'with call, use ()
                            MySub a$, b%        'without call, no ()
     

Flow Control

     if (expr) then ... elseif ... elseif ... else ... end if
     select case (expr) ... case ... case is ... end case
     on (expr) gosub
     on (expr) goto

     for var=start to end ... next var

     Do unless|until (expr)  ... Loop
     Do  ... Loop unless|until expr

     while (expr) ... wend

     gosub
     goto 

     stop, end, exit, return, system    # Program/Loop redirection
     

Functions (commonly used, built-in functions)

     Conversion  cint, cdbl, csng, clng                # number to type
                 cvd, cvi, cvs, cvl, cvsmbf, cvdmbf    # string to type

     Arithmetic  let, swap, clear        # assignment
                 data, read restore      # program data
                 exp, log, sqr           # logarithms
                 hex$, oct$              # conversions
                 abs, sgn, fix, mod, int # conversions
                 rnd, randomize          # random

     Strings     ucase$, lcase$              # capitalize
                 val, len                    # string variable properties
                 asc, chr$                   # single character functions
                 left$, right$               # truncate
                 ltrim$, rtrim$              # remove end spaces
                 mid$, instr                 # find/replace
                 rset, lset                  # justification
                 space$, string$             # return lengths of strings
                 cvi, cvl, cvs, cvd          # convert numbers to strings
                 str$, mkd$, mki$, mks$      # convert numbers to strings
                 mkdmbf$, mkl$, mksmbf$      # convert numbers to strings
                 let, swap, clear            # assignment

     Trig        atn, cos, sin, tan      # standard trigonometry functions

     Arrays      ubound, lbound        # properties
                 erase                 # reset values
                 option base           # set minimum index

     Time        date$, time$          # properties
                 timer, sleep, wait    # intervals

     Printing    lprint, lprint using    # print commands
                 lpos, spc, tab, width   # modifiers
     

Files/Directories

     bload, bsave, def seg         # binary actions
     lock, unlock                  # access control
     open, close                   # file access directive
     freefile, clear, eof, reset   # file status
     kill, name                    # file management
     write, print, print using     # write to file
     input, input$, line input     # read from file     
     get, field, put, seek         # random file actions
     files, loc, lof, fileattr     # file information
     chdir, mkdir, rmdir           # directories

     open "myfile.txt" for input as #1
     close #1

     read 1 line of file using scalar   line input#1, var$ 
     read all lines into array          while not eof(1)
                                           var$ = line input #1
                                        wend
     write line into file               print #1, var$
     write line into file (formatted)   write#1, var1$, var2

     chdir, mkdir, rmdir           # directories
     

Keyboard

     input, input$, line input     # keyboard input
     inkey$, key, key(n), On Key   # individual keystrokes
     

Sound

     play, beep, sound         # create sounds
     on play, play             # event trapping
     

Screen (Text)

     width, view print, screen, color       # properties
     csrlin, pos, locate                    # cursor status
     print, print using, write              # write to screen
     tab, spc                               # print modifiers
     

Screen (Graphics)

     screen, window, view, pmap      # mode/coordinates
     color, palette, palette using   # color control
     cls, pcopy                      # page control
     circle, line                    # define shapes
     draw, paint                     # custom shapes/fill
     pset, preset, point             # points
     get, put                        # screen image capture/display
     

Event Trapping

     on strig, strig, stick       # joystick
     on key, key                  # keyboard
     on pen, pen                  # light pen
     on com, com                  # serial ports
     on play, play, beep, sound   # speaker
     on timer, timer              # timers
     ioctl, ioctl$                # device control strings
     

Errors

     tron, troff           # trace execution
     erdev, erdev$         # device identification
     erl, err              # error information
     error                 # error simulation
     on error, resume      # error trapping
     

System Calls

     environ, environ$          # access environmental variables
     fre                        # available string space
     inp, out                   # port access
     peek, poke                 # memory access
     shell, chain, common, run  # transfer control/pass variables
     varptr, varptr$, varseg    # pointers
     call absolute              # call assembly language program
     

If you have any suggestions for additions to this mini-tutorial, please let me know.