I'm hoping to basically put in anything that's in the .NET math library, so exponents and sines should be in. As for user-defined functions, I wasn't planning for them, but if you want to add functions, the program is designed to be extensible so you can code them yourself if you know a .NET language such as C#
Basically, I have an Expression class with subclasses for all the different types of expressions there can be (unary operations, constants, functions, etc.) and to add a function you'd have to derive a class from one of my base classes and implement its Value property which does the actual computation.
If I ever get this working I'll post it on
www.codeproject.com; my main problem is to get the input string parsed out into an expression tree... but I've read about converting to Reverse Polish Notation and that should prove helpful with everything except the functions... and the (non-user-defined) functions shouldn't be too much after that, it's just a matter of getting them to take multiple parameters...