c++ 类的继承与派生 随便写的练习

#include <iostream>
using namespace std;
const double pi = 3.14;
class Point
{
protected:
    double x,y;
public:
    Point( double xx = 0, double yy = 0 ): x(xx), y(yy) {}
    void SetPoint( double a, double b )
    {
        x = a;
        y = b;
    }
    double GetX()
    {
        return x;
    }
    double GetY()
    {
        return y;
    }
    friend ostream & operator << ( ostream &output, const Point &p )
    {
        output << "[" << p.x << "," << p.y << "]" << endl;
        return output;
    }
};
class Circle:public Point
{
protected:
    double r;
public:
    Circle( double xx = 0, double yy = 0, double rr = 0 ):Point( xx, yy ),r(rr) {}
    void SetR( double rr )
    {
        r = rr;
    }
    double GetR()
    {
        return r;
    }
    double Area()
    {
        double ans = pi * r * r;
        return ans;
    }
    friend ostream & operator << ( ostream &output, const Circle &c )
    {
        output << "[" << c.x << "," << c.y << "]" << ' ' << c.r <<  endl;
        return output;
    }
};
class Cyclinder:public Circle
{
protected:
    double height;
public:
    Cyclinder( double xx  = 0, double yy = 0, double rr = 0, double hh = 0):Circle(xx, yy, rr), height(hh) {}
    void SetHeght( double hh )
    {
        height = hh;
    }
    double GetHeight()
    {
        return height;
    }
    double Area()
    {
        return 2.0 * Circle::Area() + 2 * pi * r * height;
    }
    double volume()
    {
        return Circle::Area() * height;
    }
    friend ostream& operator << ( ostream &output, Cyclinder& cy )
    {
        output << "[" << cy.x << "," << cy.y << "]" << "r = " << cy.r << " area = " << cy.Area() << " volume = " << cy.volume() << endl;
        return output;
    }
};
int main()
{
    Point a(1,2);
    double x = a.GetX();
    double y = a.GetY();
    cout << a << endl;
    cout << x << ' ' << y << endl;
    Circle c(1,2,3);
    cout << c << endl;
    double area = c.Area();
    cout << area << endl;
    Cyclinder c1(3.5,6.4,5.2,10);
    cout << c1 << endl;
    return 0;
}