课程首页在：http://blog.csdn.net/sxhelijian/article/details/11890759。内有完整教学方案及资源链接
【项目1 - 点、圆的关系】
（1）先建立一个Point(点)类。包括数据成员x,y(坐标点)；
（2）以Point为基类。派生出一个Circle(圆)类，添加数据成员(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，推断点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;
}
參考解答：
#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); //推断点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;
} //推断点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;
}
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