QBASIC/QB64 subset interpreter by Ed Davis.
----------------------------------------------------------------------------------
Currently supports:

Double and string variables only. No dim for these.
One or two dimensional arrays.
All standard operators, with hopefully the correct precedence.

String operators:
+
=, <>, <, >, <=, >=


Numeric binary operators
^,
*, /
\
mod,
+, -,
shl,<<, shr,>>
=, <>, <, >, <=, >=,
and,
or,
xor,
eqv,
imp,

Numeric unary operators
not, -, +

Commands supported:

bye, quit - exits the interpreter
clear     - clears variables
dump      - shows info about arrays
edit      - edits the current or default program
files     - shows a list of files
help      - simple help screen
list      - lists current program
list vars - iists variables
load, old - loads a program into the interpreter
new       - discards the current program
reload    - reloads the current program from disk
run       - runs the current program
save      - saves the current program
ston      - turns stepping on
stoff     - turns stepping off
tron      - turns tracing on
troff     - turns tracing off

Statements:

Iteration:
  do [while|until]
    stmts
  loop

  or

  do
    stmts
  loop [while|until]

  exit do

  while stmts wend - exit while

  for index = n to expr [step n]
  next

  exit for

Control transfer:
  gosub, return
  goto - buggy if you jump outside of loops or multiline if

Selection:
singleline or multiline if
  if elseif else end if

const - declare numeric or string constants

dim - declares double or string arrays

end, stop, system - exits program to interpreter

Other commands:

chdir circle cls color draw environ input line locate mid$ paint
palette play preset print, ? pset randomize rem screen shell
sleep sound swap view width window

QB64 commands:

_delay _display _freeimage _fullscreen _limit _printstring
_screenmove _title

Numeric functions:

abs acos acosh acot acoth acsc acsch asc asec asech asin asinh
atanh atn, atan cdbl cint clng cos cosh cot coth csc csch csng
csrlin cvd cvi exp false frac fix instr int len ln log log10 peek
point pos rnd screen sec sech sgn sin sinh sqr, sqrt tan tanh
timer true ubound val

QB64 Numeric functions:

_atan2 _ceil _d2g _d2r _fontwidth _fontheight _g2d _g2r _height
_instrrev _keydown _keyhit _mousebutton _mouseinput _mousex
_mousey _newimage _pi _r2d _r2g _rgb _rgba _rgba32 _rgb32 _round
_width

String Functions:

chr$ command$ date$ environ$ hex$ inkey$ lcase$ left$" lpad$
ltrim$ mid$ mki$ oct$ replace$ right$ rpad$ rtrim$ space$ str$
string$ time$ trim$ ucase$

QB64 string functions:

_clipboard$ _cwd$ _os$ _startdir$ _title$ _trim$

No other numeric data types besides double. Only suffix accepted is $ for strings.
Only one or two dimensional arrays
No subs or functions.
No dim.
Lots of other stuff missing.

You can run a single line of code at the ">" prompt:

>n=1:lim=25:while n<=lim:k=3:p=1:n=n+2:while k*k<=n and p:p=(n\k)*k<>n:k=k+2:wend:while p:print n; " is prime":exit while:wend:wend

You'll get:

  3 is prime
  5 is prime
  7 is prime
  11 is prime
  13 is prime
  17 is prime
  19 is prime
  23 is prime

Or you can just use it as a fancy calculator:

>3 + 4/(2*3*4) - 4/(4*5*6) + 4/(6*7*8) - 4/(8*9*10) + 4/(10*11*12) - 4/(12*13*14)
3.1408

To run an example:

Start the interpreter

You'll get a prompt.  type:  run filename
For example:

>run matrix.bas

Or:

>load matrix.bas
>run

To edit a program, type "edit".  If no program is loaded, it will edit "default.bas".
It uses notepad.exe by default, unless the EDITOR environment variable is defined, in which case it will use whatever that points to.

You can single step:

>load matrix.bas
>tron
>ston
>run

Press enter to keep on stepping

After a run, you can show variables:

>list vars

I'm sure there are lots of bugs^H^H^H^Hfeatures, so beware!

The interpreter:

Sample programs:
Fireworks by Ken G.


Snake by Johnno and BPlus


Laser Show by Sierra Ken:



Matrix by unknown:


A Tiny Basic interpreter - very limited