（提示：此任务可以分为三个子任务分成若干步骤进行。先声明基类，再声明派生类，逐级进行，分步调试。——这种方法适用于做任何的项目）
运行代码：
/*
*Copyright (c)2014,烟台大学计算机与控制工程学院
*All rights reserved.
*文件名称：d.cpp
*作 者：张旺华
*完成日期：2015年6月1日
*版 本 号：v1.0
*/
#include <iostream>
using namespace std;
const double pi=3.1415926;
class Point
{
public:
Point (double X=0,double Y=0):x(X),y(Y){}
~Point();
void setPoint(double,double);
double getx()const {return x;};
double gety()const {return y;};
friend ostream &operator<<(ostream &output,Point & p);
protected:
double x,y;
};
Point::~Point()
{}
void Point::setPoint(double a,double b)
{
x=a;
y=b;
}
ostream &operator<<(ostream &output,Point & p)
{
output<<"["<<p.x<<","<<p.y<<"]";
return output;
}
class Circle:public Point
{
public :
Circle(double a=0,double b=0,double r=0);
~Circle();
void setCircle(double a,double b,double r);
friend ostream &operator<<(ostream &output,Circle & c);
protected:
double R,area,girth;
};
Circle::~Circle(){}
void Circle::setCircle(double a,double b,double r)
{
Point(a,b);
R=r;
area=pi*R*R;
girth=pi*R*2;
}
Circle::Circle(double a,double b,double r):Point(a,b),R(r)
{
area=pi*R*R;
girth=pi*R*2;
}
ostream &operator<<(ostream &output,Circle & c)
{
output<<"R="<<c.R<<" Center=["<<c.x<<", "<<c.y<<"], r="<<c.R<<" area="<<c.area<<" girth="<<c.girth;
}
int main()
{
Circle c(3.5,6.4,5.2);
cout<<"original circle:\nx="<<c.getx()<<", y="<<c.gety()<<endl;
c.setPoint(5,5);
cout<<"new circle:\n"<<c;
return 0;
}
知识点运用及学习心得：
我在这里遇到问题就是在构造函数时候没有处理好，造成bug 。真是悲哀呀。
原文：http://blog.csdn.net/wh201458501106/article/details/46314263
