源程序：

#include <iostream>
#include <cmath>
using namespace std;class Point
{
private:
  double x, y;
public:
  Point(double a, double b)
  {
    x = a;
    y = b;
  }
  double distance()
  {
    double len;
    len = sqrt(x*x+y*y);
    return len;
  }
  friend double dis_point2(Point &,Point &);
};double dis_point2(Point &s1, Point &s2)
{
  double t_x = s1.x - s2.x;
  double t_y = s1.y - s2.y;
  double t_xy = sqrt(t_x * t_x + t_y * t_y);
  return t_xy;
}int main()
{
  Point p1(2.5, 6.3), p2(5.5,9.0);
  cout << "p1到原点的距离为："<<p1.distance() << endl;
  cout << "p2到原点的距离为：" <<p2.distance() << endl;
  cout << "p1到p2的距离为："<<dis_point2(p1, p2) << endl;
  system("pause");
  return 1;
}

运行结果：