Go: package main

import (
        "fmt"
        "math/big"
)

func main() {
        var x1, x2, x3, x4, y1, y2, y3, y4 big.Float
        var n int
        fmt.Scanf("%d", &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)
                var lx, ly, mx, my, mul1, mul2, sub, zz big.Float
                lx.Sub(&x2, &x1)
                ly.Sub(&y2, &y1)
                mx.Sub(&x4, &x3)
                my.Sub(&y4, &y3)
                mul1.Mul(&lx, &my)
                mul2.Mul(&ly, &mx)
                sub.Sub(&mul1, &mul2)
                zz.SetFloat64(0.0)

                if sub.Cmp(&zz) == 0 {
                        fmt.Println("YES")
                } else {
                        fmt.Println("NO")
                }
        }
}

C++: #include<iostream>
#include<stdio.h>
#include<math.h>
#include<string>
#include<algorithm>
#include<utility>
using namespace std;
double zeti(double);
int main() {
    pair<double,double> a;
    pair<double,double> b;
    pair<double,double>c;
    pair<double,double>d;
    int n;
    cin>>n;
    for(int i=0;i<n;++i){
        scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&a.first,&a.second,&b.first,&b.second,&c.first,&c.second,&d.first,&d.second);
        if(a.first==b.first&&c.first==d.first){
            cout<<"YES"<<endl;
            continue;
        }
        
        if((a.second-b.second)/(a.first-b.first)==(c.second-d.second)/(c.first-d.first)){
            cout<<"YES"<<endl;
        }
        else{
            cout<<"NO"<<endl;
            
        }
    }
    
    
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

int main() {
  int n;
  cin >> n;

  for(int i = 0; i < n; i++) {
    double x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

    double X1 = x2-x1, Y1 = y2-y1;
    double X2 = x4-x3, Y2 = y4-y3;

    //    printf("%lf\n", abs(X1*Y2-X2*Y1));
    if((double)abs(X1*Y2-X2*Y1) < 1e-20) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
}

C++: #include <iostream>

int main()
{
	long double x1, y1, x2, y2, x3, y3, x4, y4;
	int num_of_instance;
	std::cin >> num_of_instance;
	for (int i=0; i<num_of_instance; i++) {
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		long double tAB = (y2-y1) / (x2-x1);
		long double tCD = (y4-y3) / (x4-x3);
		if (tAB == tCD) std::cout << "YES" << std::endl;
		else std::cout << "NO" << std::endl;
	}
	return 0;
}

C++: 
#include <iostream>
#include <complex>
#include <cmath>

using namespace std;

typedef complex<double> Point;

bool parallel(const Point &v1, const Point &v2) {
    return abs(v1.real()*v2.imag() - v1.imag()*v2.real()) < 1e-10;
}

int main() {
    int N;
    cin >> N;
    while(N--) {
        Point ps[4];
        for(int i = 0; i < 4; ++i) cin >> ps[i].real() >> ps[i].imag();
        Point v1 = ps[1]-ps[0], v2 = ps[3]-ps[2];

        if(parallel(v1, v2) && !parallel(v1, ps[2]-ps[1])) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return 0;
}

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

int main(){
    const double EPS = 1e-12;
    double x[5];
    double y[5];
    double s;
    double t;
    double u;
    double v;
    double m;
    int n;
    cin >> n;

    for(int i = 0;i < n;i++){
        cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

        s = x[1] - x[0];
        t = y[1] - y[0];
        u = x[3] - x[2];
        v = y[3] - y[2];

        if(s * v - t * u > 0){
            m = s * v - t * u;
        }
        else{
            m = t * u - s * v;
        }

        if(m < EPS){
            cout << "YES" << endl;
        }
        else{
            cout << "NO" << endl;
        }
    }
    return 0;
}

C++: #include <fstream>
#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
using namespace std;

int main() {
  // ifstream cin("../test.txt");
  int n;
  cin >> n;
  while (n--) {
    double x[4], y[4];
    for (int i = 0; i < 4; i++) {
      cin >> x[i] >> y[i];
    }

    string res;
    double d = (x[1] - x[0]) * (y[3] - y[2]) - (x[3] - x[2]) * (y[1] - y[0]);
    if (d > -0.0000001 && d < 0.0000001) {
      res = "YES";
    } else {
      res = "NO";
    }
    cout << res << endl;
  }
}

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

int main() {
	int n;
	cin >> n;
	for(int i = 0; i < n; i++) {
		for(int j = 0; j < 8; j++) {
			string str;
			cin >> str;
			int k = str.find('.');
			if(str.size()-1 - k > 5)
				abort();
		}
		cout << "YES" << endl;
	}
}

C++: #include <complex>
#include <cmath>
#include <vector>
#include <cstdio>
#include <iostream>
using namespace std;

typedef complex<double> xy_t;

double dot_product(xy_t a, xy_t b) { return (conj(a)*b).real(); }
double cross_product(xy_t a, xy_t b) { return (conj(a)*b).imag(); }
xy_t projection(xy_t p, xy_t b) { return b*dot_product(p,b)/norm(b); }

const double eps = 1e-11;
// (|a|+|b|+|c|+|d|)*epsilon??¨(10-5)^2???????????°

int main(){
  int n;
  cin >> n;
  for(int i=0; i<n; ++i){
    xy_t P[4];
    double x, y;
    for(int j=0; j<4; ++j){
      cin >> x >> y;
      P[j] = xy_t(x, y);
    }
    bool p = abs(cross_product(P[1]-P[0], P[3]-P[2])) < eps;
    cout << (p ? "YES" : "NO") << endl;
  }
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include<bits/stdc++.h>
using namespace std;
#ifndef FAST_IO
 #define IOS ios_base::sync_with_stdio(false);cin.tie(nullptr);
#endif

#define FILE_IO freopen("input.txt","r",stdin)
#define int long long
#define f first
#define s second
#define endl '\n'
#define all(c) c.begin(),c.end()
#define bp __builtin_popcount
#define debug(x) cerr << #x << " = " << x << endl;

const int MOD = 1e9 + 7;
const int INF = 1e18;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T>void print(T t){for(auto &it : t)cout<<it<<" ";}
inline int powerexp(int a, int b, int m = MOD){ int res = 1;while(b){if(b&1)res = res * a % m;a = a * a % m,b >>= 1;}return res % m;}
inline int modinv(int a){ return powerexp(a,MOD-2,MOD);}
inline int lcm(int a, int b){ int g = __gcd(a,b);return a/g*b;}
inline int add(int x, int y){ x += y; if (x >= MOD) x -=  MOD; return x;}
inline int mul(int x, int y){ return (x * 1ll * y) % MOD;}
inline int sub(int x, int y){ x -= y; if (x<0) x += MOD; return x ;}

//-------------------< start here >-------------------------// 

void solve(){
   int n;
   cin >> n;
   while(n--){
	 double x[4], y[4];
	 for(int i = 0; i < 4; i++){
		  cin >> x[i] >> y[i]; 
		}
	 if (fabs((x[3] - x[2]) * (y[1] - y[0]) - (x[1] - x[0]) * (y[3] - y[2])) < 1e-10){
		  cout << "YES" << endl;
		}
	 else cout << "NO" << endl; 
	 }
}

//-----------------------------
//comment from here for TOPCODER 
int32_t main(){
   IOS;
   solve();
   //find();
   #ifdef LOCAL_DEFINE
   cerr << "time elapsed " << (double)clock()/CLOCKS_PER_SEC << endl;
   #endif
}

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

int main()
{
	int n ;
	double ax,ay,bx,by,cx,cy,dx,dy ;

	cin >> n ;
	for( int i = 0 ; i < n ; i ++ )
	{
		cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy ;

		double a = (ay-by)/(ax-bx) ;
		double b = (cy-dy)/(cx-dx) ;

		if( a == b ) cout << "YES" << endl ;
		else	cout << "NO" << endl ;
	}
	return 0 ;
}