Something

#include <iostream>

class mammal{
public:
	virtual void speak() const { std::cout << "Mammal speak\n"; }
};

class dog : public mammal{
public:
	void speak() const { std::cout << "Dog speak\n"; }
};

int main(void)
{
 mammal* m;
 mammal* d;

 m = new mammal;
 d = new dog;

  m->speak();
  d->speak();

  return 0;
}