c++纯虚函数

#include<iostream.h>class shape{public:virtual void printArea() =0;};class Rectangle:public shape  //矩形{private:double l,k,h;public:virtual void printArea(){cout<<"矩形面积="<<l*k*h<<endl;}Rectangle(double a =0,double b=0,double c=0){l=a;k=b;h=c;}};class Circle:public shape{private:double r;public:virtual void printArea() {cout<<"圆面积="<<3.1415926*r*r<<endl;}Circle(double a=0){r=a;}};class Triangle:public shape{private:double d,h;public:virtual void printArea(){cout<<"三角面积="<<d*h*0.5<<endl;}Triangle(double a=0,double b=0){d=a;h=b;}};int main(){Circle c(5);Triangle t(5,5);Rectangle r(5,5,5);shape *pt=&c;pt->printArea();pt=&t;pt->printArea();pt=&r;pt->printArea();return 0;}