2015年第十二周项目四:点，圆类的关系

（5）在圆类上重载关系运算符（6种），使之能够按圆的面积比较两个圆的大小。自编main函数完成测试。

[参考解答]

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1. #include <iostream>  
2. #include<Cmath>  
3. using namespace std;  
4. class Point  
5. {  
6. public:  
7.     Point(double a=0,double b=0):x(a),y(b) {}       //构造函数  
8. protected:                                       //受保护成员  
9.     double x,y;  
10. };  
11.   
12. class Circle:public Point //circle是Point类的公用派生类  
13. {  
14. public:  
15.     Circle(double a=0,double b=0,double r=0): Point(a,b),radius(r) { }//构造函数  
16.     double area ( ) const; //计算圆面积  
17.     friend ostream &operator<<(ostream &,const Circle &);//重载运算符“<<”  
18.     //重载关系运算符运算符，使之能够按圆的面积比较两个圆的大小；  
19.     bool operator>(const Circle &);  
20.     bool operator<(const Circle &);  
21.     bool operator>=(const Circle &);  
22.     bool operator<=(const Circle &);  
23.     bool operator==(const Circle &);  
24.     bool operator!=(const Circle &);  
25. protected:  
26.     double radius;  
27. };  
28.   
29. //计算圆面积  
30. double Circle::area( ) const  
31. {  
32.     return 3.14159*radius*radius;  
33. }  
34.   
35. //重载运算符“<<”，使之按规定的形式输出圆的信息  
36. ostream &operator<<(ostream &output,const Circle &c)  
37. {  
38.     output<<"Center=["<<c.x<<", "<<c.y<<"], r="<<c.radius;  
39.     return output;  
40. }  
41.   
42. //重载关系运算符（种）运算符，使之能够按圆的面积比较两个圆的大小；  
43. bool Circle::operator>(const Circle &c)  
44. {  
45.     return (this->radius - c.radius) > 1e-7;  
46. }  
47.   
48. bool Circle::operator<(const Circle &c)  
49. {  
50.     return (c.radius - this->radius) > 1e-7;  
51. }  
52.   
53. bool Circle::operator>=(const Circle &c)  
54. {  
55.     return !(*this < c);  
56. }  
57.   
58. bool Circle::operator<=(const Circle &c)  
59. {  
60.     return !(*this > c);  
61. }  
62.   
63. bool Circle::operator==(const Circle &c)  
64. {  
65.     return abs(this->radius - c.radius) < 1e-7;  
66. }  
67.   
68. bool Circle::operator!=(const Circle &c)  
69. {  
70.     return abs(this->radius - c.radius) > 1e-7;  
71. }  
72.   
73. int main( )  
74. {  
75.     Circle c1(3,2,4),c2(4,5,5);      //c2应该大于c1  
76.     cout<<"圆c1( "<<c1<<" )的面积是 "<<c1.area()<<endl;  
77.     cout<<"圆c2( "<<c2<<" )的面积是 "<<c2.area()<<endl;  
78.     cout<<"圆c1 ";  
79.     if(c1>c2) cout<<"大于, ";  
80.     if(c1<c2) cout<<"小于, ";  
81.     if(c1>=c2) cout<<"大于等于, ";  
82.     if(c1<=c2) cout<<"小于等于, ";  
83.     if(c1==c2) cout<<"等于, ";  
84.     if(c1!=c2) cout<<"不等于, ";  
85.     cout<<"圆c2"<<endl;  
86.   
87.     return 0;  

1. }  

2. #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    double area();    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    bool operator>(Circle &c);    bool operator<(Circle &c);    bool operator==(Circle &c);    bool operator>=(Circle &c);    bool operator<=(Circle &c);    bool operator!=(Circle &c);protected:    double radius;};bool Circle::operator>(Circle &c){    if(this->area()>c.area())return true;    else return false;}bool Circle::operator==(Circle &c){    if(this->area()==c.area())return true;    else return false;}bool Circle::operator<(Circle &c){    if(this->area()<c.area())return true;    else return false;}bool Circle::operator>=(Circle &c){    if(this->area()>=c.area())return true;    else return false;}bool Circle::operator<=(Circle &c){    if(this->area()<=c.area())return true;    else return false;}bool Circle::operator!=(Circle &c){    if(this->area()!=c.area())return true;    else return false;}double Circle::area(){    double areas;    areas=3.14159*radius*radius;    return areas;}//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),c2(4,5,5);      //c2应该大于c1    cout<<"圆c1( "<<c1<<" )的面积是 "<<c1.area()<<endl;    cout<<"圆c2( "<<c2<<" )的面积是 "<<c2.area()<<endl;    cout<<"圆c1 ";    if(c1>c2) cout<<"大于, ";    if(c1<c2) cout<<"小于, ";    if(c1>=c2) cout<<"大于等于, ";    if(c1<=c2) cout<<"小于等于, ";    if(c1==c2) cout<<"等于, ";    if(c1!=c2) cout<<"不等于, ";    cout<<"圆c2"<<endl;    return 0;}