判断两直线是否相交 hdu1086

#include <iostream>
#include <cstdio>

using namespace std;

struct line
{
    double x1;
    double y1;
    double x2;
    double y2;
}l[110];

bool test(int i,int j)
{
    int s=0;
    double acd = (l[j].x1-l[i].x1)*(l[j].y1-l[j].y2) - (l[j].x1-l[j].x2)*(l[j].y1-l[i].y1);
    double bcd = (l[j].x1-l[i].x2)*(l[j].y1-l[j].y2) - (l[j].x1-l[j].x2)*(l[j].y1-l[i].y2);
    if(acd*bcd<=0)
        s++;
    double abd = (l[i].x1-l[j].x1)*(l[i].y1-l[i].y2) - (l[i].x1-l[i].x2)*(l[i].y1-l[j].y1);
    double abc = (l[i].x1-l[j].x2)*(l[i].y1-l[i].y2) - (l[i].x1-l[i].x2)*(l[i].y1-l[j].y2);
    if(abd*abc<=0)
        s++;
    if(s==2)
        return true;
    return false;
}

int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        if(n==0)
            break;
        for(int i=0;i<n;i++)
        {
            scanf("%lf%lf%lf%lf",&l[i].x1,&l[i].y1,&l[i].x2,&l[i].y2);
        }
        int ans=0;
        for(int i=0;i<n-1;i++)
        {
            for(int t=i+1;t<n;t++)
            {
                if(test(i,t))
                    ans++;
            }
        }
        cout<<ans<<endl;
    }
    return 0;
}