How can I parse a numeric operation containing +,-,*,/ and parentheses and return the result?

Question

Possible Duplicate:
Best algorithm for evaluating a mathematical expression?

I mean like when you enter this in Delphi:

var i : integer;
begin
  i=5 + 5 + (2 * (3 + 2)) + (1 * 4 + (1 - 3))
end;

But I want a command that works in this way:

var i : integer; s:string;
begin
  s:='5 + 5 + (2 * (3 + 2)) + (1 * 4 + (1 - 3))';
  i:=ParseInt(s);
end;

Thanks in advance

This is a basic problem in compiler/interpreter methods, though you don't need the full tool kit. Check [Learning to write a compiler](http://stackoverflow.com/questions/1669/) for an exhaustive list of resource. I'd like to recomend the Crenshaw tutorial for this problem, though you will have to adapt the compiler to a interpreter. — dmckee --- ex-moderator kitten, Sep 11 '10 at 14:34

score 2 · Answer 1 · answered Sep 11 '10 at 11:49

2

If you want to implement this yourself, have a look at recursive descent parses and the shunting yard algorithm.

answered Sep 11 '10 at 11:49

IVlad

lkessler · Answer 2 · 2010-09-11T15:48:24.120

1

There are a number of free or inexpensive Math Parser components available for Delphi:

Foreval is open source, available as a DLL or delphi component.

TbcParser is $19.95 with source code.

edited Sep 11 '10 at 15:48

answered Sep 11 '10 at 15:31

lkessler

2 Answers2