1359  外部函数作友元
#include
#include
#include
using namespace std;
class point
{
    double x,y;
public:
    point(double xx,double yy)
    {     x=xx; y=yy;    }
    friend double dist(point,point);
};
double dist(point p1,point p2)
{    return sqrt(  (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)  );   }
int main()
{   int n;
    double x1,x2,y1,y2;
    cin>>n;
    while (n--)
    {   cin>>x1>>y1>>x2>>y2;
        point p1(x1,y1),p2(x2,y2);
        cout<
    }
}
1359  类的成员函数作友元
#include
#include
#include
using namespace std;
class point;
class test
{public:
 double dist(point,point);    
};
class point
{   double x,y;
public:
    point(double xx,double yy)
    {     x=xx; y=yy;    }
    friend double test::dist(point,point);
};
double test::dist(point p1,point p2)
{    return sqrt(  (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)  );   }
int main()
{   int n;   double x1,x2,y1,y2; test t;
    cin>>n;
    while (n--)
    {   cin>>x1>>y1>>x2>>y2;
        point p1(x1,y1),p2(x2,y2);
        cout<
    }
}
1359  友元类（类的所有成员函数作友元）
#include
#include
#include
using namespace std;
class point;
class test
{public:
 double dist(point,point);    
};
class point
{   double x,y;
public:
    point(double xx,double yy)
    {     x=xx; y=yy;    }
    friend class test;
};
double test::dist(point p1,point p2)
{    return sqrt(  (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)  );   }
int main()
{   int n;   double x1,x2,y1,y2; test t;
    cin>>n;
    while (n--)
    {   cin>>x1>>y1>>x2>>y2;
        point p1(x1,y1),p2(x2,y2);
        cout<
    }
}