#include <iostream>

/*
g++ virtualexample.cpp and use ./a.out to run.
*/
class A{
    public:

    virtual void p(){
        std::cout << "A.p\n";
    }
    void q(){
        std::cout << "A.q\n";
    }

    virtual void r(){
        p();
        q();
    }
};

class B : public A{

    public:

    void p(){
        std::cout << "B.p\n";
    }
};

class C : public B{
    public:

    void q(){
        std::cout << "C.q\n";
    }

    void r(){
        q();
        p();
    }
};

int main(){
    A a;
    C c;
    a = c;
    a.r();
    A* ap = new B;
    ap->r();
    ap = new C;
    ap->r();

    return 0;
}

Output:
A.p
A.q
B.p
A.q
C.q
B.p