写一个程序，定义抽象基类Shape，由它派生出3个派生类: Circle(圆形)、Rectangle(矩形)、Triangle(三角形)

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写一个程序，定义抽象基类Shape，由它派生出3个派生类: Circle(圆形)、Rectangle(矩形)、Triangle(三角形)，用一个函数printArea分别输出以上三者的面积，3个图形的数据在定义对象时给定。

#include<iostream>using namespace std;class Shape{public:virtual float printArea() const {return 0.0;};};class Circle:public Shape{public: Circle(float =0); virtual float printArea() const {return 3.14159*radius*radius;}protected:float radius;};Circle::Circle(float r):radius(r){}class Rectangle:public Shape{public:Rectangle(float =0,float =0);virtual float printArea() const;protected:float height;float width;};Rectangle::Rectangle(float w,float h):width(w),height(h){}float Rectangle::printArea()const{return width*height;}class Triangle:public Shape{public:Triangle(float =0,float =0);virtual float printArea() const;protected:float height;float width;};Triangle::Triangle(float w,float h):width(w),height(h){}float Triangle::printArea()const{return 0.5*width*height;}void printArea(const Shape&s){cout<<s.printArea()<<endl;}int main(){Circle circle(12.6);cout<<"area of circle=";printArea(circle);Rectangle rectangle(4.5,8.4);cout<<"area of rectangle=";printArea(rectangle);Triangle triangle(4.5,8.4);cout<<"area of triangle=";printArea(triangle);}

用基类指针数组，使它每个元素指向一个派生类对象，求面积之和。

Shape *p[3]={&circle,&rectangle,&triangle};double area=0.0;for(int i=0;i<3;i++) {area+=p[i]->printArea();}cout<<"total of all area= "<<area;

area of circle=498.759
area of rectangle=37.8
area of triangle=18.9
total of all area= 555.459
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Process exited after 0.4691 seconds with return value 0
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