Many years ago I've written an VB app to solve polynomials and draw graphs for them, key part of that project were routines for calculating simpler math stuff with keeping the proper order of performing mathematical operations. And that basically this code is, a simple math parser.

How to use it? First init with 'GOSUB math_parser_init', add your custom variables like 'x' with 'mp_add_iconst("x", 21)', and then just calculate with 'parse_math_cmd$(your_string$)' (you can also add custom functions) for example:

`GLOBAL user_str$, x_val$ // for inputed stuff`

GOSUB math_parser_init

PRINT "Please type x value:", 10, 10

INPUT x_val$, 10, 20

mp_add_iconst("x", x_val$)

PRINT "Write equation below", 10, 30

INPUT user_str$, 10, 40

user_str$ = parse_math_cmd$(user_str$)

PRINT "result: " + user_str$, 10, 50

DEBUG "result: " + user_str$

SHOWSCREEN

MOUSEWAIT

END

You can use this for gui positioning/animations: button.left = integer(parse_math_cmd$("screen_width-20"))

or more advanced calculator app: result = parse_math_cmd$("2sin(0.5)+3(pi+int(1.1))-fps")

and so on...