Any libraries to interpret mathematical expressions?

[Chemical Engineer]

Say that I have a string, char equation[] = "=7*x+2*ln(PI)", and I want to evaluate it using something like double Eqvaluate(char equation[100]). Are there any libraries to do this with (i.e., as Excel does)?

Also, are there any libraries to take derivatives or find integrals (i.e., as Mathematica does)?

[moorecm]

I'm not aware of any specific libraries, although I'd bet they are out there.

Boost.Spirit can be used to write a parser:
http://www.boost.org/doc/libs/1_43_0/libs/spirit/doc/html/index.html

Here are some applications that use it, a few of which can evaluate basic algebraic expressions:
http://boost-spirit.com/repository/applications/show_contents.php

The Interpreter pattern could also be implemented to perform similar evaluations.