第13周项目3—形状类族中的纯虚函数

#include <iostream>
#include <string>
using namespace std;
class Shape
{
public:
virtual double area()=0;
};
class Circle:public Shape
{
public:
Circle(double r)
{
this->r=r;
}
double area()
{
return 3.14*r*r;
}
private:
double r;
};
class Rectangle:public Shape
{
public:
Rectangle(double a,double b)
{
this->a=a;
this->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 a*b*0.5;
}
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;
}