断忆风的博客

#include <iostream> using namespace std; class base { public: virtual float area() const { return 0; } }; class triangle: public base { protected: float bian,height; public: triangle(float a=0, float h=0) { bian=a; height=h; } virtual float area() const { return bian*height/2; } }; class square: public base { protected: float bian; public: square(float a=0) { bian=a; } virtual float area() const { return bian*bian; } }; class circle: public base { protected: float radius; public: circle(float r=0) { radius=r; } virtual float area() const { return 3.14*radius*radius; } }; int main() { triangle t(3,4); square s(5); circle c(2); base *p; p=&t; cout<<"triangle's area:"<<p->area()<<endl; p=&s; cout<<"square's area:"<<p->area()<<endl; p=&c; cout<<"circle's area:"<<p->area()<<endl; return 0; }