The following Visual Basic project contains the source code and Visual Basic examples used for expression evaluator (string calculator). I think many of you have asked for such a thing. You give it a string like "2+3^(5-3*SIN(18-5^2))/SQR(2)+LOG(8)" .. etc. And it returns the result of calculation.
The source code and files included in this project are listed in the project files section, please make sure whether the listed source code meet your needs there.