list1409.cpp

teach yourself C++ in 21 days 第五版

//Listing 14.9 Implementing pure virtual functions

#include <iostream>
using namespace std;

class Shape
{
  public:
    Shape(){}
    virtual ~Shape(){}
    virtual long GetArea() = 0; // error
    virtual long GetPerim()= 0;
    virtual void Draw() = 0;
  private:
};

void Shape::Draw()
{
   cout << "Abstract drawing mechanism!\n";
}

class Circle : public Shape
{
  public:
    Circle(int radius):itsRadius(radius){}
    virtual ~Circle(){}
    long GetArea() { return 3.14 * itsRadius * itsRadius; }
    long GetPerim() { return 2 * 3.14 * itsRadius; }
    void Draw();
  private:
    int itsRadius;
    int itsCircumference;
};

void Circle::Draw()
{
   cout << "Circle drawing routine here!\n";
   Shape::Draw();
}


class Rectangle : public Shape
{
  public:
    Rectangle(int len, int width):
    itsLength(len), itsWidth(width){}
    virtual ~Rectangle(){}
    long GetArea() { return itsLength * itsWidth; }
    long GetPerim() {return 2*itsLength + 2*itsWidth; }
    virtual int GetLength() { return itsLength; }
    virtual int GetWidth() { return itsWidth; }
    void Draw();
  private:
    int itsWidth;
    int itsLength;
};

void Rectangle::Draw()
{
   for (int i = 0; i<itsLength; i++)
   {
      for (int j = 0; j<itsWidth; j++)
         cout << "x ";

   cout << "\n";
   }
   Shape::Draw();
}


class Square : public Rectangle
{
  public:
    Square(int len);
    Square(int len, int width);
    virtual ~Square(){}
    long GetPerim() {return 4 * GetLength();}
};

Square::Square(int len):
Rectangle(len,len)
{}

Square::Square(int len, int width):
Rectangle(len,width)

{
   if (GetLength() != GetWidth())
   cout << "Error, not a square... a Rectangle??\n";
}

int main()
{
   int choice;
   bool fQuit = false;
   Shape * sp;

   while (fQuit == false)
   {
      cout << "(1)Circle (2)Rectangle (3)Square (0)Quit: ";
      cin >> choice;
 
      switch (choice)
      {
       case 1: sp = new Circle(5);
             break;
       case 2: sp = new Rectangle(4,6);
             break;
       case 3: sp = new Square (5);
             break;
       default: fQuit = true;
             break;
      }
       if (fQuit == false)
       {
          sp->Draw();
          delete sp;
          cout << endl;
       }
    }
    return 0;
 }