Well, that's what I was already planning to do, i.e. have each major function in its own file, which I then include in the main source code file. But I was hoping I could have a function within the main.cpp file that would be part of the class "main_window_form" for the purpose of adding variables to the class.
I guess I'll have to try the method matsp suggested, i.e. use a derived class for adding variables.
Thanks everyone for your help. I really appreciate it.