.. _ch12-xt5:

习题5
=======


定义抽象基类Shape
-------------------

.. code-block:: c++ 

   #include <iostream>
   #define PI 3.1415926  //定义计算圆的面积pi的值
   using namespace std; 

   class Shape
   {
   public:
      virtual double area() const = 0;
   };


定义Shape的派生类Circle(圆形)
-------------------------------

.. code-block:: c++ 

   class Circle : public Shape
   {
   public:
      Circle(double r):radius(r){}
      virtual double area() const 
      {
         return PI * radius * radius;
      }

   protected:
      double radius;
   };


定义Shape的派生类Square(正方形)
----------------------------------

.. code-block:: c++ 

   class Square : public Shape
   {
   public:
      Square(double s):side(s){}
      virtual double area() const 
      {
         return side * side;
      }
   
   protected:
      double side;
   };

定义Shape的派生类Rectangle(矩形)
-----------------------------------

.. code-block:: c++ 

   class Rectangle : public Shape
   {
   public:
      Rectangle(double h, double w):height(h),width(w){}
      virtual double area() const
      {
          return height * width;
      }
   protected:
      double height;
      double width;

   };

定义Shape的派生类Trapezoid(梯形)
-----------------------------------

.. code-block:: c++ 

   class Trapezoid: public Shape
   {
   public:
       Trapezoid(double t, double b, double h):top(t), bottom(b), height(h){}
       virtual double area() const
       {
           return (top + bottom) * height / 2;
       }
   protected:
       double top;
       double bottom;
       double height;
   };

定义Shape的派生类Triangle(三角形)
-----------------------------------
  
.. code-block:: c++ 
  
   class Triangle: public Shape
   {
   public:
      Triangle(double b, double h):bottom(b), height(h){}
      virtual double area() const
      {
          return bottom * height / 2;
      }
   protected:
      double bottom;
      double height;
   };

写main函数
------------

.. code-block:: c++ 

   int main()
   {
      Circle circle(2.4);
      Square square(4.0);
      Rectangle rectangle(3.0, 5.0);
      Trapezoid trapezoid(3.0, 2.0, 4.0);
      Triangle triangle(2.4, 5.9);

      Shape *pt[5]={&circle, &square, &rectangle, &trapezoid, &triangle};

      double areas = 0.0;
      for (int i = 0; i < 5; i++)
      {
         areas += pt[i] -> area();
      }

      cout << "总面积是：" << areas <<endl;

      return 0;
   }