Toughest concept in C++

Question

Which is the toughest concept in C++? Is it Composition (in class) ?

Answer 1

The toughest concepts are not even in the tutorials.

Answer 2

That's different for everyone. For some understanding pointers is tough, for others maybe composition. For me it's polymorphism and virtual inheritance

Answer 3

Maybe pointer and dynamic memory management?

Answer 4

what does cpp stand for in source file of a constructor?