After:

class screen
{
   public:
      screen( int, int );
      int getLength() const { return length; }
      int getWidth() const { return width; }
  
   protected:
      int length;
      int width;
};

class touchScreen: public screen
{
   public:
      touchScreen( int, int, bool );
      bool isActive() const { return active; }
  
   private:
      bool active;
};