You are using setData on object of class A , but calling compare on object of class B. Use b in both case.
int main()
{
  A a;
  B b;
  //int c;
  clrscr();
  b.setData(25,9);
  cout<<"answer: "<<b.compare();
  getch();
  return 0;
}
also change signature of main method.
3
solved C++ is not Giving Expected output [closed]