Xây dựng lớp hình tròn dẫn xuất từ lớp điểm

//************************************************************
#include <iostream>
using namespace std;

class CPOINT
{
private:
double x, y;
public:
CPOINT()
{
x = y = 0.0;
}
CPOINT(double x, double y)
{
this->x = x;
this->y = y;
}
void show_xy()
{
cout << "(x, y) = ("<< x << ", " << y << ")" << endl; } }; class CCIR : public CPOINT { private: double r; public: CCIR() { r = 0.0; } CCIR(double x, double y, double r) : CPOINT(x, y) { this->r = r;
}
void show_r()
{
cout << "r = " << r << endl;
}
};

int main ()
{
CCIR circle(2.3, -5, 6.0);
circle.show_xy();
circle.show_r();

system("pause");
return 0;
}