设计一个描述点的类，其中包含一对坐标点数据成员、一个求两个点之间距离的友元函数和显示坐标点的成员函数，并编程测试。

解题思路：

计算两点(a,b)和(c,d)之间的距离，依据勾股定理可得公式：



并定义坐标点类的友元函数来计算两点间的距离。

-Design a descr iptive point of the class, which includes a pair of coordinates of points, data members, one for the distance between two points of the Friends of element function, and display coordinates of member functions, and programming test. Problem-solving approach: calculation of two points (a, b) and (c, d) distance between the Pythagorean Theorem based on the availability of formula: and define the coordinates of points, type of friend function to calculate the distance between two points.