"classic" OO solution for birds problem

birds_classic.cpp

#include <iostream>

class Bird
{
  public:
    virtual void Fly() const = 0;
    virtual void Speak() const = 0;
};

class Eagle : public Bird
{
  public:
    virtual void Fly() const
    {
      std::cout << "Eagle shall fly now!" << std::endl;
    }
    virtual void Speak() const
    {
      std::cout << "Eagle speaking!" << std::endl;
    }
};


class Penguin : public Bird
{
  public:
    virtual void Fly() const
    {
      std::cout << "Penguin shall fly now!" << std::endl;
    }
    virtual void Speak() const
    {
      std::cout << "Penquin speaking!" << std::endl;
    }
};

int main()
{
  std::cout << "..." << std::endl;
  Bird* bird = NULL;
  
  bird = new Eagle();
  bird->Fly();
  bird->Speak();
  delete bird; bird = NULL;

  bird = new Penguin();
  bird->Fly();
  bird->Speak();
  delete bird; bird = NULL;

  return 0;
}