13周任务3

#include <iostream>
using namespace std;
class Shape
{
public:
 virtual float area() const=0;// {return 0.0;}
};
class Circle:public Shape
{
public:
 virtual float area() const;
 Circle(double r1):r(r1){}
protected:
 double r;
};
class Rectangle:public Shape
{
public:
 virtual float area() const;
 Rectangle(double L1,double L2):l1(L1),l2(L2){}
protected:
 double l1,l2;
};
class Triangle:public Shape
{
public:
 virtual float area() const;
 Triangle(double l1,double h1):l(l1),h(h1){}
protected:
 double l,h;
};

float Circle::area()const
{
 return 3.14*r*r;
}
float Rectangle::area()const
{
 return l1*l2;
}
float Triangle::area()const
{
 return (l*h)/2;
}

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，各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
 system("pause");
 return 0;

}

 感悟：1.将自己做的和老师的一比才知道，自己在定义变量时用的符号有问题，自己能看懂，别人就不一定看懂，如h和height.

2.不要忘了写构造函数啊。。。