Class A members depends on Class B members: how to?

[keskiverto]

Have you seen: http://www.cplusplus.com/doc/tutorial/polymorphism/

[dhayden]

It sounds to me like the background object should be global. After all, it's part of the context of the entire game.

Yes, yes, I know, "globals are bad," you should never use them, blah blah blah. Tell it to cin and cout. When a piece of data is part of the overall context of the program, then make it a global.