We're not human compilers. At least make an honest effort before asking us questions. What you posted has a number of mistakes and issues, and it indicates you have no clue what you're doing. Don't dump garbage code at us without giving us anything to go on.
Here's a free pass:
Go learn to code for real, and make sure you're not lazy about it. We're willing to help, of course, but if you don't have a good foundation in something, we can't point you in the right direction. That requires you to learn.
virtual void display()
std::cout << "No function display defined in this class\n";
class D : public B