OJ友元类-计算两点间距离

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
class Point;
class Distance
{
public:
float Dis(Point & p,Point & q);

};
class Point
{
public:
Point(float a,float b):x(a),y(b){}
friend class Distance;
private:
float x;
float y;
};
float Distance::Dis(Point &p,Point &q)
{
return sqrt((p.x-q.x)*(p.x-q.x)+(p.y-q.y)*(p.y-q.y));
}
int main()
{
float x1,y1,x2,y2;
cin>>x1>>y1>>x2>>y2;
Point p(x1,y1), q(x2,y2);
cout<<setiosflags(ios::fixed);
cout<<setprecision(2);
Distance d;
cout<<d.Dis(p,q)<<endl;
return 0;
}