第12周 项目四-点、圆关系（4）

（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）；

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;
}

代码：

#include <iostream>
using namespace std;
class Point
{
public:
    int x;
    int y;
public:
    Point(int a,int b):x(a),y(b) {}
    friend ostream &operator <<(ostream &out,Point &a);
};
ostream &operator <<(ostream &out,Point &a)
{
    cout<<"x="<<a.x<<" y="<<a.y<<endl;
    return out;
}
class Circle:public Point
{
protected:
    int r;
public:
    Circle(int a,int b,int c):Point(a,b),r(c) {}
    friend ostream &operator <<(ostream  &out,Circle &a);
    friend int locate(Point &a,Circle &b);
};
ostream &operator <<(ostream  &out,Circle &a)
{
    cout<<"圆心:"<<" ("<<a.x<<"<"<<a.y<<") "<<"半径:"<<a.r<<endl;
    return out;
}
int locate(Point &a,Circle &b)
{
    return (b.r*b.r-(a.x-b.x)*(a.x-b.x)-(a.y-b.y)*(a.y-b.y));
}
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;
}

运行结果：