判断线段与直线是否相交，注意精度问题。
#include<iostream>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<math.h>
using namespace std;
#define eps 0.00000001
#define zero(x) ((fabs(x)<eps)?0:x)
struct segn
{double x1,y1;double x2,y2;
}seg[110];
int n;
struct line
{int leap;double k;double b;
}ll;
int dos(line a,segn b)
{if(a.leap==1){if((a.b<=max(b.x1,b.x2)&&a.b>=min(b.x1,b.x2))||(!zero(a.b-b.x1)||!zero(a.b-b.x2)))return 1;else return 0;}double b1,b2,bb;b1=b.y1-a.k*b.x1;b2=b.y2-a.k*b.x2;bb=a.b;if((bb<=max(b1,b2)&&bb>=min(b1,b2))||(!zero(bb-b1)||!zero(bb-b2)))return 1;return 0;
}
int pan(double x1,double y1,double x2,double y2)
{if(zero(x1-x2)==0){ll.leap=1;ll.b=x1;}else{ll.leap=0;ll.b=(y1*x2/x1-y2)/(x2/x1-1);ll.k=(y1-ll.b)/x1;}for(int i=1;i<=n;i++){if(!dos(ll,seg[i]))return 0;}return 1;
}
int leap;
int main()
{int T,i,j;cin>>T;while(T--){leap=0;cin>>n;for(i=1; i<=n; i++){cin>>seg[i].x1>>seg[i].y1>>seg[i].x2>>seg[i].y2;}for(i=1;i<=n;i++){for(j=1;j<=n;j++){if(pan(seg[i].x1,seg[i].y1,seg[i].x2,seg[i].y2))leap=1;if(pan(seg[i].x1,seg[i].y1,seg[j].x2,seg[j].y2))leap=1;if(pan(seg[i].x1,seg[i].y1,seg[j].x1,seg[j].y1))leap=1;if(pan(seg[j].x1,seg[j].y1,seg[i].x2,seg[i].y2))leap=1;if(pan(seg[j].x1,seg[j].y1,seg[j].x2,seg[j].y2))leap=1;if(pan(seg[j].x2,seg[j].y2,seg[i].x2,seg[i].y2))leap=1;if(leap)break;}if(leap)break;}if(leap==1)cout<<"Yes!"<<endl;else cout<<"No!"<<endl;}return 0;
}