练习题（P135）

#include<iostream>
#include<cmath>
using namespace std;

class Point
{
private:
double x,y;
friend class Line;
public:
Point(double i =0,double j = 0)
{
x = i;
y = j;
}
Point(Point &p)
{
x = p.x;
y = p.y;
}
};

class Line
{
private:
Point p1,p2;
public:
Line(Point &xp1,Point &xp2):p1(xp1),p2(xp2){}
double GetLength();
};

double Line::GetLength()
{
double dx = p2.x - p1.x;
double dy = p2.y - p1.y;
return sqrt(dx*dx + dy*dy);
}

int main()
{
Point p1,p2(6,8);
Line L1(p1,p2);
cout<<L1.GetLength()<<endl;
return 0;
}