C++ class examples

#include <iostream>
#include <string>
using namespace std;

// Class
class Animal{
  public:
  int lifespan;
  Animal(){}
  Animal(int _lifespan){
    lifespan = _lifespan;
  }
};

// Inheritance
class Dog : public Animal{
  public:
  string say;
  Dog(string _say) : Animal(20){
    say = _say;
  }
};

// Extension
//    void Dog::whine(){
  //    cout << "*whine*" << endl
//    }
// Apparently you can't do that in C++ unless it was already declared within the class

//Instantiation
int main(){
  Dog doggy("bark");
  cout << "Dog says " << doggy.say << endl;
  cout << "Dog's lifespan is " << doggy.lifespan << endl;
  return 0;
}