Go: package main

import "fmt"

func abs(x float64) float64 {
	if x < 0 {
		return -x
	}
	return x
}

func main() {
	var n int
	var x1, y1, x2, y2, x3, y3, x4, y4 float64
	fmt.Scan(&n)
	for i := 0 ; i < n; i++ {
		fmt.Scanf("%f %f %f %f %f %f %f %f", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4)
		if abs((x2-x1)*(y4-y3) - (y2-y1)*(x4-x3)) < 1e-10 {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

C++: #include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
#include <functional>
#include <sstream>
#include <utility>
#include <cstdlib>
#include <cctype>
#include <climits>
#include <fstream>

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<pair<int, int> > vpii;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) for(int i=0;i<(n);++i)
#define foreach(itr,c) for(__typeof(c.begin()) itr=c.begin(); itr!=c.end(); itr++)
#define dbg(x) cout << #x"="<< (x) << endl
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back(a) 
#define in(x) cin >> x;
#define all(x) (x).begin(), (x).end()
#define INF 2147483600
#define fi first
#define se second
using namespace std;

int main(){
	int N;
	vd a(8);
	cin >> N;
	rep(i,N){
		rep(i,8){
			cin>>a[i];
		}
		if(((a[1]-a[3])*(a[4]-a[6])-(a[5]-a[7])*(a[0]-a[2]))<0.0000001){
			cout<<"YES"<<endl;
		}else{
			cout<<"NO"<<endl;
		}
	}

}

C++: #include<iostream>
using namespace std;

int main() {
	double x[8], y[8];
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int i = 0; i < 4; i++) {
			cin >> x[i] >> y[i];
		}
		x[0] -= x[1];
		y[0] -= y[1];
		x[2] -= x[3];
		y[2] -= y[3];
		if (x[0] * y[2] - x[2] * y[0] == 0) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
#define rrep(i,n) for(int i=n;i>=0;i--)
#define all(v) v.begin(),v.end()
template<typename T>T rad(T deg){return deg*M_PI/180;}
using namespace std;
int main() {
    int n;
    cin >> n;
    rep(j,n) {
        complex<double> a[4];
        rep(i, 4) {
            double x, y;
            cin >> x >> y;
            a[i] = *(new complex<double>(x, y));
        }
        complex<double> vAB = a[0] - a[1];
        complex<double> vCD = a[2] - a[3];
        double m1 = arg(vAB);
        double m2 = arg(vCD);
        cout << ((m1==m2) ? "YES" : "NO") << endl;
    }
}

C++: #include<iostream>
using namespace std;
int main(){
  int n;
  cin>>n;
  while(n--){
    double x1,y1,x2,y2,x3,y3,x4,y4;
    cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
    if(x1==x2&&x3==x4)cout<<"YES"<<endl;
    else if(y1==y2&&y3==y4)cout<<"YES"<<endl;
    else{
      if((y2-y1)/(x2-x1)==(y4-y3)/(x4-x3)){
	cout << "YES" << endl;
      }else cout << "NO" << endl;
    }
  }
}

C++: #include<iostream>
#include<vector>
int main()
{
	int n;
	std::cin >> n;
	std::vector<bool>result(n);
	for (int i = 0; i < n; i++)
	{
		long double x1, y1, x2, y2, x3, y3, x4, y4;
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		result[i] = x1 == x2 && x3 == x4 || (y1 - y2) / (x1 - x2) == (y3 - y4) / (x3 - x4);
	}
	for (auto i : result)
	{
		std::cout << (i ? "YES" : "NO") << std::endl;
	}
	return 0;
}

C++: #include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <complex>
#include <ctime>
#include <cstdlib>
??
using namespace std;
??
inline int to_int(string s) {int v; istringstream sin(s); sin >> v; return v;}
template<class T> inline string to_str(T x) {ostringstream sout; sout << x; return sout.str();}
??
typedef long long ll;
??
int main()
{
????????int num;
????????double sx1, sy1, sx2, sy2;
????????double ex1, ey1, ex2, ey2;
??
????????cin >> num;
??
????????for(int i = 0; i < num; i++)
????????{
????????????????cin >> sx1 >> sy1 >> sx2 >> sy2 >> ex1 >> ey1 >> ex2 >> ey2;
??
????????????????if( (sy2-sy1)/(sx2 - sx1) == (ey2-ey1)/(ex2-ex1))
????????????????{
????????????????????????cout << "YES" << endl;
????????????????}
????????????????else
????????????????{
????????????????????????cout << "NO" << endl;
????????????????}
????????}
}

C++: #include <iostream>
using namespace std;
int n;
double xa,xb,xc,xd,ya,yb,yc,yd,ta,tb,tc,td;
int main(){
	int i;
	cin >> n;
	for(i=0;i<n;i++){
		cin >> xa >> ya >> xb >> yb >> xc >> yc >> xd >> yd;
		ta = xb - xa;
		tb = yb - ya;
		tc = xd - xc;
		td = yd - yc;
		if(tb == td && ta == tc) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include<iostream>
#include<cmath>
#include<cassert>
#include<cstdlib>
using namespace std;
#define EPS 0.0000001
 
 
int main(){
  int tcase;   cin >> tcase;
  double x1, y1, x2, y2, x3, y3, x4, y4;
  for ( int i = 0; i < tcase; i++ ){
      cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
 
   
      if ( abs((y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1) ) < EPS ) cout << "YES" << endl;
      else cout << "NO" << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <deque>
#include <list>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>

using namespace std;

int n;
double x1,x2,x3,x4,ya1,y2,y3,y4;

int main() {
	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> x1 >> ya1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		/*
		if (x1 > x2) {
			double tmp = x1;
			x1 = x2;
			x2 = tmp;
			tmp = ya1;
			ya1 = y2;
			y2 = tmp;
		}
		if (x3 > x4) {
			double tmp = x3;
			x3 = x4;
			x4 = tmp;
			tmp = y3;
			y3 = y4;
			y4 = tmp;
		}
		*/

		if (x1 == x2) {
			if (x3 == x4) cout << "YES" << endl;
			else cout << "NO" << endl;
		} else {
			if (x3 == x4) cout << "NO" << endl;
			else {
				if ((y2 - ya1) / (x2 - x1) - (y4 - y3) / (x4 - x3) <= 0.00000000001)
					cout << "YES" << endl;
				else cout << "NO" << endl;
			}
		}
	}

	return 0;
}

/*@@@@@@@@@@@@@@@@@@@@@@@@@*/
/*@                       @*/
/*@ debug output erased ? @*/
/*@                       @*/
/*@@@@@@@@@@@@@@@@@@@@@@@@@*/

C++: #include <iostream>
#include <stdio.h>
using namespace std;
int main()
{
    int N;
	cin>>N;
	while(N--){
		double x1,y1,x2,y2,x3,y3,x4,y4;
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		(y1-y2)*(x3-x4)-(y3-y4)*(x1-x2)?cout<<"NO"<<endl:cout<<"YES"<<endl;
	}
    return 0;
}

C++: #include<iostream>
using namespace std;
int main() {
  int n;
  cin>>n;
  double x1,x2,x3,x4,y1,y2,y3,y4;
  for(int i=0;i<n;i++){ 
    cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
    if(x1==x2 && x3==x4)
      cout<<"YES";
    else if( ( (y2-y1)/(x2-x1) )== ( (y4-y3)/(x4-x3) ) )
      cout<<"YES";
    else
      cout<<"NO";
    cout<<endl;
  }
  return 0;
}

C++: #include<cstdio>
#include<iostream>

using namespace std;

int main(void){

	long double x1,y1,x2,y2,x3,y3,x4,y4;
	int n;

	cin>>n;

	for(int i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		if(y2-y1==0){
			if(y4-y3==0) cout<<"YES"<<endl;
			else cout<<"NO"<<endl;
		}
		else if((x2-x1)/(y2-y1)==(x4-x3)/(y4-y3)) cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}

	return 0;
}