How do I declare a string and pass it from a Visual Basic GUI to a C++ DLL?

Now I am debugging successfully. I can debug either on the Visual Basic end or I can debug on the C++ side by using the DLL's project file and declaring the compiled VB code as the launching executable. I have narrowed the problem down to the way that I am declaring and passiing the string variables.

How do I declare strings to pass from VB to C? This must be a common thing that is done often. Surely there is a sample of it somewhere.