程序代码

#include <iostream>

using namespace std;

class Point//点类
{
public:
    //使用初始化表初始化点类
    Point(double a = 0, double b = 0):x(a), y(b){}
    double getX();
    double getY();

    //重载<<实现点的坐标的输出
    friend ostream& operator<<(ostream &output, Point &p);

protected:
    double x;//横坐标
    double y;//纵坐标
};

//得到x的值
double Point::getX()
{
    return x;
}

//得到y的值
double Point::getY()
{
    return y;
}

//重载<<实现点的坐标的输出
ostream& operator<<(ostream &output, Point &p)
{
    output<<"("<<p.x<<","<<p.y<<")"<<endl;

    return output;
}


//Point派生出Circle类
class Circle : public Point
{
public:
    //构造函数(初始化半径的两个端点)
    Circle(double a, double b, double r);
    void SetRadius();//设置圆的半径
    double GetRadius();//得到圆的半径
    double getArea();//计算圆的面积
    
    //重载<<实现输出圆的面积
    friend ostream& operator<<(ostream &output, Circle &c);

protected:
    double r;//圆的半径
};

//构造函数(使用初始化表初始化Circle类)
Circle::Circle(double a, double b, double r):Point(a, b),r(r){}

//设置圆的半径
void Circle::SetRadius()
{
    this->r = r;
}

//得到圆的半径
double Circle::GetRadius()
{
    return r;
}

//计算圆的面积
double Circle::getArea()
{
    //计算圆的面积
    double s = 3.14 * r * r;

    return s;
}

//重载<<实现输出圆的面积
ostream& operator<<(ostream &output, Circle &c)
{
    output<<"圆的面积:"<<c.getArea()<<endl;

    return output;
}


void main()
{
    //定义一个圆对象
    Circle c(1.0, 2.9, 4.0);

    //输出圆的半径
    cout<<"圆的半径:"<<c.GetRadius()<<endl;

    //输出圆的面积
    cout<<c;

    system("pause");
}

执行结果

Point类派生出Circle类