2015年第十一周项目四：类族的设计（2）

#include <iostream>

using namespace std;

class Point
{
protected:
double x;
double y;
public:
Point(double,double);
Point(){}
~Point(){}
friend ostream & operator<<(ostream&,const Point &);

};
ostream& operator<<(ostream&output,const Point &p)
{
output<<"("<<p.x<<","<<p.y<<")";
return output;
}
Point::Point(double m,double n)
{
x=m;
y=n;
}
class Circle:public Point
{
protected:
double r;
public:
double area();
Circle(double m,double n,double q):Point(m,n),r(q){}
void setr(double q)
{
r=q;
}
friend ostream& operator <<(ostream&,const Circle&c);
};
ostream& operator <<(ostream&output,const Circle&c)
{
output<<"("<<c.x<<","<<c.y<<","<<c.r<<")";
return output;
}
double Circle::area()
{
return 3.14*r*r;
}
int main()
{
Circle c(5,6,9);
cout<<c;
cout<<c.area();
return 0;
}