第十二周（点圆类）

*作者：王忠
*完成日期：2015.5.27

*版本号：v1.0
*
*问题描述：（1）先建立一个Point(点)类，包含数据成员x,y(坐标点)；
（2）以Point为基类，派生出一个Circle(圆)类，增加数据成员(半径)，基类的成员表示圆心；
（3）编写上述两类中的构造、析构函数及必要运算符重载函数（本项目主要是输入输出）；
（4）定义友元函数int locate，判断点p与圆的位置关系（返回值<0圆内，==0圆上，>0 圆外）；

*输入描述：

*程序输出：

#include<iostream>
#include<Cmath>
using namespace std;
class Point //定义坐标点类
{
public:
    Point():x(0),y(0) {};
    Point(double x0, double y0):x(x0), y(y0) {};
    friend ostream& operator <<(ostream &output,Point &p);
    double distance(Point &p);
protected:
    double x,y;   //点的横坐标和纵坐标
};
class Circle:public Point
{
public:
    Circle(double x,double y,double z):Point(x,y),r(z) {}
    friend istream& operator >>(istream &input,Circle &c);
    friend ostream& operator <<(ostream &output,Circle &c);
    friend int locate(Point &p, Circle &c);
protected:
    double r;
};
ostream& operator <<(ostream &output,Point &p)
{
    output<<"Point: ("<<p.x<<","<<p.y<<")"<<endl;
    return output;
}
double Point::distance(Point &p)
{
    double dx = x-p.x;
    double dy = y-p.y;
    return sqrt(dx*dx+dy*dy);
}

istream& operator >>(istream &input,Circle &c)
{
    double a,b,d;
    cout<<"输入半径，圆心坐标：";
    input>>a>>b>>d;
    Circle(a,b,d);
    return input;
}
ostream& operator <<(ostream &output,Circle &c)
{
    output<<"Circle: ("<<c.r<<","<<c.x<<","<<c.y<<")"<<endl;
    return output;
}
int locate(Point &p,Circle &c)
{
    Point cp(c.x,c.y);
    double d = cp.distance(p);
    if (d==c.r)
        return 0;
    else if (d < c.r)
        return -1;
    else
        return 1;
}

int main( )
{
    Circle c1(3,2,4),c2(4,5,5);      //c2应该大于c1
    Point p1(1,1),p2(3,-2),p3(7,3);  //分别位于c1内、上、外
    cout<<"圆c1: "<<c1;

    cout<<"点p1: "<<p1;
    cout<<"点p1在圆c1之"<<((locate(p1, c1)>0)?"外":((locate(p1, c1)<0)?"内":"上"))<<endl;

    cout<<"点p2: "<<p2;
    cout<<"点p2在圆c1之"<<((locate(p2, c1)>0)?"外":((locate(p2, c1)<0)?"内":"上"))<<endl;

    cout<<"点p3: "<<p3;
    cout<<"点p3在圆c1之"<<((locate(p3, c1)>0)?"外":((locate(p3, c1)<0)?"内":"上"))<<endl;
    return 0;
}