Undefined symbols for architecture x86_64. what's wrong with my codes?

You commented out a bunch of function definitions in devices. Cpp (the five at the bottom). They're still in the header.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.