下面程序的输出结果是 【15】 。 #include<iostream.h> #include<math.h> class point { double x; double y; public: point(doublea,d double B) { x=a; y=b; } friend double distance (point a,point B) ; }; double distance (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<<distance(p1,p2)<<end1;}