习题5

定义抽象基类Shape

#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)

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)

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)

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)

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)

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

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;
}

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