多态的应用之几何形体处理

输入若干个几何形体的参数，要求按面积从小到大输出，并在输出中指明几何形体类型。

#include <iostream>
#include <cstdlib>
#include <cmath>using namespace std;
class CShape{
public:virtual double Area()=0;  //存虚函数,无函数体virtual void PrintInfo()=0;
};class CRectangle:public CShape{
public:int w,h;virtual double Area();virtual void PrintInfo();
};class CCircle:public CShape{
public:int r;virtual double Area();virtual void PrintInfo();
};class CTriangle:public CShape{
public:int a,b,c;virtual double Area();virtual void PrintInfo();
};double CRectangle::Area(){return w*h;
}
void CRectangle::PrintInfo(){cout<<"Rectangle:"<<Area()<<endl;
}double CCircle::Area(){return 3.14*r*r;
}
void CCircle::PrintInfo(){cout<<"Circle:"<<Area()<<endl;
}double CTriangle::Area(){double p=(a+b+c)/2.0;return sqrt(p*(p-a)*(p-b)*(p-c));
}
void CTriangle::PrintInfo(){cout<<"Triangle:"<<Area()<<endl;
}CShape* pShapes[100];
int MyCompare(const void* s1,const void* s2);
int MyCompare(const void* s1,const void* s2)
{double a1,a2;CShape** p1;  //s1,s2是void*,CShape** p2;p1=(CShape**)s1;  //s1,s2指向pShape数组中的元素，数组元素是CShape*，因此p1,p2是p2=(CShape**)s2;  //指向指针的指针，CShape**a1=(*p1)->Area();  //*p1的类型是CShape*，是基类的指针，因此是多态a2=(*p2)->Area();if(a1<a2)return -1;else if(a2<a1)return 1;elsereturn 0;
}
int main()
{int i,n;CRectangle *pr; CCircle *pc;CTriangle *pt;cin>>n;for(i=0;i<n;i++){char c;cin>>c;switch(c){case 'R':pr=new CRectangle();cin>>pr->w>>pr->h;pShapes[i]=pr;break;case 'C':pc=new CCircle();cin>>pc->r;pShapes[i]=pc;break;case 'T':pt=new CTriangle();cin>>pt->a>>pt->b>>pt->c;pShapes[i]=pt;break;}}qsort(pShapes,n,sizeof(CShape*),MyCompare);for(i=0;i<n;i++){pShapes[i]->PrintInfo();  //多态}return 0;
}

输出样例：

案例来自北京大学网络课堂《C++程序设计》