C++ regex

[camelCase]

I decided to try writing a calculator like the one on Google and it works perfectly; almost.
It reads mathematical expressions correctly until I try and nest parentheses for function calls..

For example:
Input: cos(0)
Output String: (cos(0))
Evaluates To: 1

Input: cos((0))
Output String:
Evaluates To: 0

I've tracked the bug down to this line:

    static regex expression_token(
        string("(\\d+\\.\\d+)|")+  //Number followed by period followed by number
        "(\\d+\\.)|"+              //Number followed by period
        "(\\.\\d+)|"+              //Period followed by number
        "(\\d+)|"+                  //Number with no period
        "(\\()|"+                  //Open parentheses
        "(\\))|"+                  //Close parentheses
        "([^\\dA-Za-z]+)|"+        //An operator
        "([A-Za-z0-9_]*)"+          //Func name
            "\\("+                  //Open <---
            "([^\\(\\)]*)"+        //Args <--
            "\\)"                  //Close <--
    );

The lines commented as "Open", "Args" and "Close" are the problem.
As you can see, I do not allow nested parentheses for function calls.
I didn't allow them because I wouldn't know when the end of the argument list would be.

So..
Is there a way, using regex, to specify.. Uh..
"I want there to be the same amount of open and close parentheses inside the arg list" ?

The "Open" line is the beginning of the argument list and the "Close" line is the end of the argument list. So, the "Args" line is all that needs changing, I guess.

I'm just not sure if regex can count characters and stuff.

 

[GFreak45]

iterate through the list and count them, or create a linked list and push each "(" into the front of it, then remove them as you run into ")"s, if you have any "(" left over or run into a ")" when there are no "("s in the linked list then they have an invalid ammount of parenthesis

I myself was looking at creating a calculator that would handle un-known variables, etc, as text, basically an algebraic calculator, that was my "first C++ project" and that was the solution i came up with for the same problem, its nice because using that method you can link each parenthesis to the correct counterpart without iterating through it a bunch of times, just once. O(n) rather than O(n*log(n)) which is the more simple method of iterating through it and expanding each parenthesis then iterating again

 

[camelCase]

My current solution is O(n); it just doesn't handle nested parentheses in function calls =x
(Unless regex isn't a linear algorithm..)
Guess I'll have to change my approach for this, then..

Oh, well.
Thanks.