第十三周 项目1 确定点在圆上的位置（补发）

#include <iostream>
#include<Cmath>
using namespace std;
class Point
{
public:
    Point(double a=0,double b=0):x(a),y(b) {} //构造函数
    double distance(const Point &p) const;	//求距离
    friend ostream & operator<<(ostream &,const Point &);//重载运算符“<<”
protected:	  //受保护成员
    double x,y;
};

double Point::distance(const Point &p) const	//求距离
{
    double dx = x-p.x;
    double dy = y-p.y;
    return sqrt(dx*dx+dy*dy);
}

ostream & operator<<(ostream &output,const Point &p)
{
    output<<"["<<p.x<<","<<p.y<<"]"<<endl;
    return output;
}

class Circle:public Point //circle是Point类的公用派生类
{
public:
    Circle(double a=0,double b=0,double r=0) :Point(a,b),radius(r) { }; //构造函数
    friend ostream &operator<<(ostream &,const Circle &);//重载运算符“<<”
    friend int locate(const Point &p, const Circle &c); //判断点p在圆上、圆内或圆外，返回值：<0圆内，==0圆上，>0 圆外
protected:
    double radius;
};

//重载运算符“<<”，使之按规定的形式输出圆的信息
ostream &operator<<(ostream &output,const Circle &c)
{
    output<<"Center=["<<c.x<<", "<<c.y<<"], r="<<c.radius<<endl;
    return output;
}

//判断点p在圆内、圆c内或圆c外
int locate(const Point &p, const Circle &c)
{
    const Point cp(c.x,c.y); //圆心
    double d = cp.distance(p);
    if (abs(d - c.radius) < 1e-7)
        return 0;  //相等
    else if (d < c.radius)
        return -1;  //圆内
    else
        return 1;  //圆外
}

int main( )
{
    Circle c1(3,2,4);
    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;
}

运行结果