index.cpp for polymorphism

#include <iostream>
#include <vector>
#include <memory>
using namespace std;

class Animal {
  public:
        string name;
        Animal (const std::string& givenName) : name(givenName) {

        }
    string speak () {
      return "";
    }

  };

class Dog: public Animal {
  public:
        Dog (const std::string& givenName) : Animal (givenName) {

        }
    string speak ()
      { return "Woof, woof!"; }
  };

class Cat: public Animal {
  public:
        Cat (const std::string& givenName) : Animal (givenName) {
        }
    string speak ()
      { return "Meow..."; }
  };

int main() {
        std::vector<std::unique_ptr<Animal>> animals;
        animals.push_back( new Dog("Skip") );
        animals.push_back( new Cat("Snowball") );

        for( int i = 0; i< animals.size(); ++i ) {
                cout << animals[i]->name << " says: " << animals[i]->speak() << endl;
        }

}