text: #include <iostream>
  #include <string>
  #include<cassert>
  using namespace std;
  
  //By: Gianluca Venditti
  //Date: November 22nd 2021
  //Specification file that defines all the classes
  
  class Package
  {
  public:
  	Package();
  	Package(string /*source*/, string /*destination*/);
  	virtual ~Package();
  	virtual double computeShipCost() const { return 0.0; }
  	string getSource() const { return *source; }
  	string getDestination() const { return *destination; }
  
  protected:
  	string* source;
  	string* destination;
  };
  
  class Letter : public Package
  {
  public:
  	Letter();
  	Letter(int /*number of pages*/, string /*source*/, string /*destination*/);
  	double computeShipCost() const;
  	int getNoPages()const { return noPages; }
  
  private:
  	int noPages;
  };
  
  class Box : public Package
  {
  public:
  	Box();
  	Box(int /*weight*/, string /*source*/, string /*destination*/);
  	double computeShipCost() const;
  	int getWeight() const { return weight; }
  
  private:
  	int weight;
  };