类的组合与继承
（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、析构函数及必要的输入输出函数
（4）定义友元函数int locate。推断点p在圆c上、圆c内或圆c外。返回值<0圆内，==0圆上，>0 圆外；
（5）重载关系运算符（6种）运算符，使之可以按圆的面积比較两个圆的大小；

程序代码

#include <iostream>
#include <cmath>using namespace std;class Point//点类
{
public://构造函数Point(double a = 0, double b = 0);//得到点的x坐标double GetX();//得到点的y坐标double GetY();//重载<<运算符实现输出点的坐标friend ostream& operator<<(ostream &output, Point &p);protected:double x;double y;
};//构造函数
Point::Point(double a, double b):x(a), y(b){}//得到点的x坐标
double Point::GetX()
{return x;
}//得到点的y坐标
double Point::GetY()
{return y;
}//重载<<运算符实现输出点的坐标
ostream& operator<<(ostream &output, Point &p)
{output<<"("<<p.x<<","<<p.y<<")"<<endl;return output;
}//Point类派生出Circle类
class Circle : public Point
{
public://构造函数Circle(double a = 0, double b = 0, double r = 0);//得到圆的半径double GetR();//推断点p与圆c的位置friend int locate(Point p, Circle c);//计算圆的面积double GetArea();//输出圆的信息friend ostream& operator<<(ostream &output, Circle &c);//重载>运算符,用于比較两个圆的面积的大小friend bool operator>(Circle &c1, Circle &c2);//重载<运算符,用于比較两个圆的面积的大小friend bool operator<(Circle &c1, Circle &c2);//重载==运算符,用于比較两个圆的面积的大小friend bool operator==(Circle &c1, Circle &c2);//重载!=运算符,用于比較两个圆的面积的大小friend bool operator!=(Circle &c1, Circle &c2);//重载>=运算符,用于比較两个圆的面积的大小friend bool operator>=(Circle &c1, Circle &c2);//重载<=运算符,用于比較两个圆的面积的大小friend bool operator<=(Circle &c1, Circle &c2);protected:double r;//半径
};//构造函数
Circle::Circle(double a, double b, double r):Point(a, b), r(r){}//得到圆的半径
double Circle::GetR()
{return r;
}//得到圆的面积
double Circle::GetArea()
{return 3.14 * r * r;
}//推断点p与圆c的位置
int locate(Point p, Circle c)
{double d;//保存点到圆心的距离double r;//保存圆的半径double flag;//标示位//计算点到圆心的距离d = sqrt((p.GetX() - c.GetX()) * (p.GetX() - c.GetX()) + (p.GetY() - c.GetY()) * (p.GetY() - c.GetY()));//得到圆的半径r = c.GetR();if(d > r )//点在圆外{flag = 1;}else if(d == r)//点在圆上{flag = 0;}else//点在圆内{flag = -1;}return flag;
}//输出圆的信息
ostream& operator<<(ostream &output, Circle &c)
{output<<"("<<c.GetX()<<","<<c.GetY()<<")"<<" r = "<<c.GetR()<<endl;return output;
}//重载>运算符,用于比較两个圆的面积的大小
bool operator>(Circle &c1, Circle &c2)
{if(c1.GetArea() > c2.GetArea()){return true;}else {return false;}
}//重载<运算符,用于比較两个圆的面积的大小
bool operator<(Circle &c1, Circle &c2)
{if(c1.GetArea() < c2.GetArea()){return true;}else {return false;}
}//重载==运算符,用于比較两个圆的面积的大小
bool operator==(Circle &c1, Circle &c2)
{if(!(c1 > c2) && !(c1 < c2)){return true;}else {return false;}
}//重载!=运算符,用于比較两个圆的面积的大小
bool operator!=(Circle &c1, Circle &c2)
{if( !(c1 == c2)){return true;}else{return false;}
}//重载>=运算符,用于比較两个圆的面积的大小
bool operator>=(Circle &c1, Circle &c2)
{if( (c1 == c2) || (c1 > c2)){return true;}else{return false;}
}//重载<=运算符,用于比較两个圆的面积的大小
bool operator<=(Circle &c1, Circle &c2)
{if( (c1 == c2) || (c1 < c2)){return true;}else{return false;}
}void main( )
{Circle c1(3,2,4),c2(4,5,5);      //c2应该大于c1Point 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; cout<<endl; cout<<"圆c1: "<<c1; if(c1>c2) cout<<"大于"<<endl; if(c1<c2) cout<<"小于"<<endl; if(c1>=c2) cout<<"大于等于"<<endl; if(c1<=c2) cout<<"小于等于"<<endl; if(c1==c2) cout<<"等于"<<endl; if(c1!=c2) cout<<"不等于"<<endl; cout<<"圆c2: "<<c2; cout<<endl; system("pause"); }

运行结果