点类上 加圆类

/* *Copyright(c)2016,LynseyListening *All rights reserced. *文件名称：listening.cpp *作者    ：陈旭 *完成日期：2016.5.14 *版本号  ：codeblocks 16.01*/#include <iostream>using namespace std;class point{protected:    double x;    double y;public:    point(double x=0,double y=0);    void setpoint(double a,double b);    void showpoint();};point::point(double a,double b){    x=a;    y=b;}void point::setpoint(double a,double b){    x=a;    y=b;}void point::showpoint(){    cout<<x<<"--"<<y<<endl;}class cricle:public point{public:    cricle(double x=0,double y=0,double r=1);    void set_r(double);    void showcircle();    void area();protected:    double r;};cricle::cricle(double a,double b,double c){    x=a;    y=b;    r=c;}void cricle::set_r(double x){    r=x;}void cricle::showcircle(){    cout<<"圆心："<<x<<","<<y<<"    "<<"r="<<r<<endl;}void cricle::area(){    cout<<"area="<<3.14*r*r<<endl;}int main( ){    cricle sn(1,2,3);    sn.showcircle();    sn.area();    sn.set_r(3.3);    sn.showcircle();    sn.area();    return 0;}

运行结果：

<img src="http://img.blog.csdn.net/20160514160650777" alt="" />