NO9——线段相关

 #include <stdio.h>
 #include <iostream>
 #include <math.h>
 #include <algorithm>
 using namespace std;

 struct point
 {
     double x,y;
 };
 point a[][];//a[i][0]代表第i条线段的头，a[i][1]代表尾

 double fan(double x,double y)
 {
     return x>y?x:y;
 }

 double fin(double c,double d)
 {
     return c<d?c:d;
 }

 double cnt(point a,point b)
 {
     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
 }

 int is(point a,point b,point c,point d)
 {
     if(a.x==b.x&&c.x==d.x)
     {
         return ;
     }
     if(a.x==b.x&&c.x!=d.x)
     {
         double m1=a.x;
         double m2=(a.x-c.x)*(d.y-c.y)/(d.x-c.x)+c.y;
         if(m1<=fan(a.x,b.x)&&m1>=fin(a.x,b.x)&&m2>=fin(a.y,b.y)&&m2<=fan(a.y,b.y)&&m1<=fan(c.x,d.x)&&m1>=fin(c.x,d.x)&&m2>=fin(c.y,d.y)&&m2<=fan(c.y,d.y))
             return ;
     }
     if(c.x==d.x&&a.x!=b.x)
     {
         double m1=c.x;
         double m2=a.y+(b.y-a.y)*(c.x-a.x)/(b.x-a.x);
         if(m1<=fan(a.x,b.x)&&m1>=fin(a.x,b.x)&&m2>=fin(a.y,b.y)&&m2<=fan(a.y,b.y)&&m1<=fan(c.x,d.x)&&m1>=fin(c.x,d.x)&&m2>=fin(c.y,d.y)&&m2<=fan(c.y,d.y))
             return ;
     }
     double k1=(b.y-a.y)/(b.x-a.x);
     double k2=(d.y-c.y)/(d.x-c.x);
     double m1,m2,x,y;
     if(k1==k2)  return ;
     else
     {
         m1=a.y-k1*a.x;
         m2=c.y-k2*c.x;
         x=(m1-m2)/(k2-k1);
         y=k1*x+m1;
         if(x<=fan(a.x,b.x)&&x>=fin(a.x,b.x)&&y>=fin(a.y,b.y)&&y<=fan(a.y,b.y)&&x<=fan(c.x,d.x)&&x>=fin(c.x,d.x)&&y>=fin(c.y,d.y)&&y<=fan(c.y,d.y))
             return ;
     }
     return ;
 }

 int main()
 {
     int cas = ;
     int n,i,j;
     while(~scanf("%d",&n),n)
     {
         int cnt = ;
         for(i = ;i<n;i++)
         scanf("%lf%lf%lf%lf",&a[i][].x,&a[i][].y,&a[i][].x,&a[i][].y);//线段的首尾坐标
         for(i = ;i<n;i++)
         {
             for(j = i+;j<n;j++)
             {
                 if(is(a[i][],a[i][],a[j][],a[j][]))
                 cnt++;
             }
         }
         printf("%d\n",cnt);
     }

     return ;
 }