14_3Shape

#include <iostream>using namespace std;class Shape{public:    virtual double area() const =0;};class Circle:public Shape{public:    Circle(double r):radius(r) {}    virtual double area() const    {        return 3.14159*radius*radius;    };protected:    double radius;};class Rectangle:public Shape{public:    Rectangle(double l,double w):L(l),W(w){}    virtual double area()const    {return L*W;}private:    double L,W;};class Triangle:public Shape{public:    Triangle(double l,double h):L(L),H(h){}    virtual double area()const    {return L*H*0.5;    };private:    double L,H;};int main(){    Circle c1(12.6),c2(4.9);//建立Circle类对象c1,c2,参数为圆半径    Rectangle r1(4.5,8.4),r2(5.0,2.5);//建立Rectangle类对象r1,r2,参数为矩形长、宽    Triangle t1(4.5,8.4),t2(3.4,2.8); //建立Triangle类对象t1,t2，参数为三角形底边长与高    Shape *pt[6]= {&c1,&c2,&r1,&r2,&t1,&t2}; //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<6; i++)    {        areas=areas + pt[i]->area();    }    cout<<"totol of all areas="<<areas<<endl;   //输出总面积    return 0;}