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 <iomanip>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <numeric>
#include <iterator>

using namespace std;

typedef long long LL;
typedef unsigned long long ULL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int,int> PII;
typedef vector<PII> VPII;
typedef istringstream ISS;
typedef ostringstream OSS;

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); ++i )
#define FOR( v, c ) for ( auto &v : c )
#define EACH( it, c ) for ( auto it = c.begin(); it != c.end(); ++it )
#define ALL( c ) (c).begin(), (c).end()
#define DRANGE( c, p ) (c).begin(), (c).begin() + p, (c).end()

#define PB( n ) push_back( n )
#define MP( a, b ) make_pair( ( a ), ( b ) )
#define EXIST( c, e ) ( (c).find( e ) != (c).end() )

#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl
#define DEBUG( x ) cerr << __FILE__ << ":" << __LINE__ << ": " << #x << " = " << ( x ) << endl

#include <complex>
typedef complex<double> Point;
const double EPS = 1e-8;

// 入力ストリームから実数二つをとって Point へ
istream& operator >> ( istream &s, Point &a )
{
	double r, i;
	s >> r >> i;
	a = Point( r, i );
	return s;
}

// a == b
bool eq( const double a, const double b )
{
	return abs( a - b ) <= EPS;
}


// 外積（クロス積）
double cross( const Point &a, const Point &b )
{
	return a.real() * b.imag() - a.imag() * b.real();
}

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );

	int n;
	cin >> n;
	REP( i, 0, n )
	{
		Point a, b, c, d;
		cin >> a >> b >> c >> d;
		cout << ( eq( cross( a - b, c - d ), 0 ) ? "YES" : "NO" ) << endl;
	}

	return 0;
}

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

typedef complex<double> xy_t;
double x[4], y[4];

const double EPS = 1e-11;
int main()
{
    int N;
    cin >> N;
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < 4; j++) {
            cin >> x[i] >> y[i];
        }
        if (abs((y[1] - y[0])*(x[3] - x[2]) - (y[3] - y[2])*(x[1] - x[0])) < EPS)cout << "YES" << endl;
        else cout << "NO" << endl;
    }
    return 0;
}

C++: #include <iostream>

int main() {
	int n;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	std::cin >> n;

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


}