（3）再以Circle類為直接基類，派生出一個Cylinder(圓柱體)類，再增加資料成員h(高)，，以及求圓柱表面積的成員函式area和求圓柱體積的成員函式volume，實現需要的成員函式，並設計main函式完成測試。

程式碼

#include<iostream>
#include<Cmath>
using namespace std;
class Point
{
protected:
    double x,y;
public:
    Point(double xx,double yy):x(xx),y(yy){}
    double getx()
    {
        return
 
 x;
    }
    double gety()
    {
        return y;
    }
    void show1();
};
void Point::show1()
{
    cout<<"底面圓心座標:"<<"("<<x<<","<<y<<")"<<endl;
}
class Circle:public Point
{
protected:
    double r,area;
public:
    Circle(double xx,double yy,double rr):Point
 
(xx,yy),r(rr){}
    double getarea();
    void show2();
    double getr()
    {
        return r;
    }
};
double Circle::getarea()
{
    area=r*r*3.14;
    return area;
}
void Circle::show2()
{
    show1();
    cout<<"底面積:"<<getarea()<<endl;
}
class Cylinder:public Circle
{
protected
 
:
    double h,volume;
public:
    Cylinder(double xx,double yy,double rr,double hh):Circle(xx,yy,rr),h(hh){}
    double getvolume();
    friend ostream &operator<<(ostream &out,Cylinder &c);
    double geth()
    {
        return h;
    }
};
double Cylinder::getvolume()
{
    volume=getarea()*h;
    return volume;
}
ostream &operator<<(ostream &out,Cylinder &c)
{
    c.show2();
    out<<"體積:"<<c.getvolume()<<endl;
    return out;
}
int main()
{
    Cylinder c(2.2,3.3,4.4,5.5);
    cout<<"該圓柱體的屬性:"<<endl;
    cout<<"底面半徑:"<<c.getr()<<endl;
    cout<<"高:"<<c.geth()<<endl;
    cout<<c;
    return 0;
}

執行結果：