6.12

#include<iostream>using namespace std;class area_cl{protected:double height;double width;public:area_cl(double a,double b){height=a;width=b;}virtual double area()=0;};class rectangle:public area_cl{public:rectangle(double a,double b):area_cl(a,b){}double area(){return height*width;}};class ioscseles:public area_cl{public:ioscseles(double a,double b):area_cl(a,b){ }double area(){return 0.5*height*width;}};int main(){area_cl* p;rectangle A(10.0,5.0);ioscseles B(4.0,6.0);p=&A;cout<<"矩形面积为："<<p->area()<<endl;p=&B;cout<<"三角形面积为:"<<p->area()<<endl;}