1 #include<cstdio>
 2 #include<cmath>
 3 using namespace std;
 4 #define eps 1e-6
 5 #define N 105
 6 struct point{
 7     double x , y ;
 8     point(double x_, double y_){
 9          x = x_;
10          y = y_;
11     }
12     point(){}
13     point operator - (const point a) const
14     {
15         return point(x-a.x,y-a.y);
16     }
17     double operator * (const point a) const
18     {
19         return x*a.y - a.x*y;
20     }
21 };
22 
23 struct line{
24     point s , t;
25 }L[N];
26 
27 int main()
28 {
29     int T;
30     while(~scanf("%d",&T),T)
31     {
32         for(int i = 0 ;i < T ; i++)
33         {
34             scanf("%lf%lf%lf%lf",&L[i].s.x,&L[i].s.y,&L[i].t.x,&L[i].t.y);
35         }
36         int ans = 0;
37         for(int i = 0 ; i < T ; i++)
38         {
39             for(int j = i+1 ; j < T ; j++)//j从i开始保证不会重复判断
40             {
41                // if(i==j) continue;
42                 point A = L[i].s;
43                 point B = L[i].t;
44                 point C = L[j].s;
45                 point D = L[j].t;
46                 if((((D-C)*(A-C))*((D-C)*(B-C)))>eps) {continue;}
47                 if((((D-A)*(B-A))*((C-A)*(B-A)))>eps) {continue;}
48                     ans++;
49             }
50         }
51         printf("%d\n",ans);
52     }
53     return 0;
54 }

 1 #include <cstdio>
 2 #include <cmath>
 3 using namespace std;
 4 #define eps 1e-8
 5 #define N 105
 6 struct point{
 7     double x, y;
 8     point(){}
 9     point(double _x, double _y) {
10         x = _x, y = _y;
11     }
12     
13     point operator - (point a){
14         return point(x-a.x, y-a.y);
15     }
16     
17     double operator * (point a){
18         return x*a.y - y*a.x;
19     }
20 };
21 
22 struct line{
23     point s, t;
24 }L[N];
25 
26 bool ck(line a, line b)
27 {
28     point A = a.s, B = a.t, C = b.s, D = b.t;
29     if(((C-A)*(B-A)) *((D-A)*(B-A)) > eps) return false;
30     if(((A-C)*(D-C)) *((B-C)*(D-C)) > eps) return false;
31     return true;
32 }
33 
34 int main()
35 {
36     int n;
37     while(~scanf("%d", &n), n)
38     {
39         for(int i = 0; i < n; i++)
40             scanf("%lf %lf %lf %lf", &L[i].s.x, &L[i].s.y, &L[i].t.x, &L[i].t.y);
41         int cnt = 0;
42         for(int i = 0; i < n; i++)
43             for(int j = i+1; j < n; j++)
44                 cnt += ck(L[i], L[j]);
45         printf("%d\n", cnt);
46     }
47 }