第六章第六题

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#include <iostream>using namespace std;//定义抽象基类Shapeclass Shape{public: virtual double area() const =0;                                //纯虚函数};//定义Circle(圆形)类class Circle:public Shape{public:Circle(double r):radius(r){}                                     //结构函数  virtual double area() const {return 3.14159*radius*radius;};   //定义虚函数 protected:  double radius;                                                 //半径};//定义Square(正方形)类class Square:public Shape{public:  Square(double s):side(s){}                                     //结构函数  virtual double area() const {return side*side;}                //定义虚函数 protected:  double side;};//定义Rectangle(矩形)类class Rectangle:public Shape{public: Rectangle(double w,double h):width(w),height(h){}               //结构函数 virtual double area() const {return width*height;}              //定义虚函数 protected:  double width,height;                                           //宽与高};//定义Trapezoid(梯形)类class Trapezoid:public Shape{public:  Trapezoid(double t,double b,double h):top(t),bottom(t),height(h){} //结构函数  virtual double area() const {return 0.5*(top+bottom)*height;}      //定义虚函数 protected:  double top,bottom,height;                                          //上底、下底与高};//定义Triangle(三角形)类class Triangle:public Shape{public:  Triangle(double w,double h):width(w),height(h){}                //结构函数  virtual double area()const {return 0.5*width*height;}          //定义虚函数 protected:  double width,height;                                            //宽与高};int main(){ Circle circle(10.6);                                             //建立Circle类对象circle Square square(3.5);                                              //建立Square类对象square Rectangle rectangle(2.5,8.4);                                    //建立Rectangle类对象rectangle Trapezoid trapezoid(2.0,4.5,3.2);                                //建立Trapezoid类对象trapezoid Triangle triangle(4.5,8.4);                                      //建立Triangle类对象 Shape *pt[5]={&circle,&square,&rectangle,&trapezoid,&triangle};                                                //定义基类指针数组pt，使它每一个元素指向一个派生类对象 double areas=0.0;                                                //areas为总面积 for(int i=0;i<5;i++)  {areas=areas+pt[i]->area();} cout<<"总面积="<<areas<<endl;   //输出总面积 return 0;}
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