// The solution to the problem just encountered. The function members
// named operation in the classes A and B must be virtual.


#include <iostream>
#include <string>

using namespace std;

class A {
public:
  int data;

  virtual int operation(){
     cout << "A: operation" << endl;
     return data;
  }
};


class B {
public:
  int data;

  virtual int operation(){
     cout << "B: operation" << endl;
     return data;
  }
};


class C: public A, public B{
public: 
  int operation() override {    
     cout << "C: operation" << endl;
     int r1 = A::operation(),
         r2 = B::operation();
     return r1 + r2;     
  }
};


int f(A* obj){
  int res = obj->operation();
  return res;
}


int main(){
  A *obj = new C();
  f(obj);   // OUTPUT:
            // C: operation
            // A: operation
            // B: operation
}