十四周项目2

#include<iostream>
using namespace std;
#define PI 3.1415926
class Shape{
public:
    virtual double area()=0;
};
class Circle:public Shape{
public:
   Circle(double r):r(r){}
   double area(){
  return PI*r*r;
}
private:
    double r;

};
class Rectangle:public Shape{
public:
    Rectangle(double a,double b):a(a),b(b){}
    double area(){
    return a*b;
    }

private:
    double a,b;

};
class Triangle:public Shape{
public:
    Triangle(double a,double b):a(a),b(b){}
    double area(){
    return 1/2*a*b;
    }

private:
double a,b;
};
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;
}

 运行结果：