4.22

<pre name="code" class="cpp">#include<iostream>  
#include<cmath>  
using namespace std;  
class point  
{ 
private: 
    int x;  
    int y;  
public:  
    point(int m,int n);                   //声明构造函数
    friend void dist(point &a,point &b);  //声明函数dist为类point的友元函数
    void show()  
    {  
        cout<<"点的坐标是：("<<x<<","<<y<<")"<<endl;               
    }  
};  
     point::point(int m,int n)            //定义构造函数，给x、y赋初值
	{ x=m;
	  y=n;
	}
void dist(point &a,point &b)              //定义友元函数dist，形参是point类对象的应用
  {  
     float d;  
     int d1=a.x-b.x;  
     int d2=a.y-b.y;  
     d=sqrt(d1*d1+d2*d2);  
     cout<<"两点间距离为："<<d<<endl;  
  }  
int main()  
  {  
    point a1(1,1);  
    point b1(2,2);  
    a1.show();  
    b1.show();  
    dist(a1,b1);  
    return 0;  
  }