懵逼了，主函数老是出现未定义标识符的错误。分析和运行下面的程序，注意友元函数dist(point a,point b)的作用。将友元函数dist(point a,point b)改为Point类的公有成员函数Point ::dist(point &b)，请修改主函数中的相应代码，使程序功能不变。#include <iostream>#include <cmath>using namespace std;class Point{ double x; double y;public: Point(double a,double b) { x=a; y=b; } friend double dist(Point a,Point b);};double dist(Point a,Point b){ return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}void main(){ Point p1(1,2); Point p2(5,2); cout<<dist(p1,p2)<<endl;}