继承与派生，重载<<

///继承与派生

#include <iostream>

using namespace std;

class Point {
public:
    Point (float a=0,float b=0):x(a),y(b) {}    ///有默认参数的构造函数
    void setPoint (float,float);    ///重新设置坐标

    ///读x的坐标，getX为常成员函数，只能访问类的数据，而不能更改
    float getX() const {
        return x;
    }

    float getY() const {
        return y;
    }

    ///友元函数重载<<
    friend ostream & operator << (ostream &,const Point &);
protected:
    float x,y;
};

void Point::setPoint(float m,float n) {
    x=m;
    y=n;
}

ostream & operator << (ostream & output,const Point &p) {
    output<<"["<<p.x<<","<<p.y<<"]"<<endl;
    return output;
}


class Circle:public Point {
public:
    Circle (float a=0,float b=0,float r=0):Point(a,b),radius(r) {}

    void setRadius(float);    ///重置半径
    friend ostream & operator << (ostream &,const Circle &);
private:
    float radius;
};

ostream & operator << (ostream & output,const Circle & c) {
    output<<"["<<c.x<<","<<c.y<<"]"<<" r="<<c.radius<<endl;
    return output;
}

int main() {
    Point p(1.0,3.5);
    cout<<p.getX()<<" "<<p.getY()<<endl;

    p.setPoint(8.5,5.6);
    cout<<p<<endl;

    Circle a(14.5,45.5,4);
    cout<<a<<endl;
    return 0;
}