判断2个线段是否相交

#include<bits/stdc++.h>
using namespace std;
#define  ll long long
struct zb
{
    double x,y;
}a,b,c,d;
double en(zb a,zb b,zb c)
{
    double m1=(a.x-b.x)*(a.y-c.y);
    double m2=(a.y-b.y)*(a.x-c.x);
    return m1-m2;
}
int main()
{
   int t;
   cin>>t;
   while(t--)
   {
       cin>>a.x>>a.y;
       cin>>b.x>>b.y;
       cin>>c.x>>c.y;
       cin>>d.x>>d.y;
       double t1=en(a,b,c);
       double t2=en(a,b,d);
       double t3=en(c,d,a);
       double t4=en(c,d,b);
       if(t1*t2<=0&&t3*t4<=0)cout<<"Yes\n";
       else cout<<"No\n";

   }
}