P225 5

<img src="http://img.blog.csdn.net/20150610194047520?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvWXVTb25nNDg2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />#include <iostream> using namespace std;//定义抽象基类Shape class 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(12.6); //建立Circle类对象circle   Square square(3.5); //建立Square类对象square   Rectangle rectangle(4.5,8.4);//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<<"totol of all areas="<<areas<<endl;//输出总面积return 0; }