Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextInt() int {
	scanner.Scan()
	i, e := strconv.Atoi(scanner.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func main() {
	n := nextInt()
	for i := 0; i < n; i++ {
		scanner.Scan()
		points := strings.Split(scanner.Text(), " ")
		fpoints := make([]float64, 0)
		for _, v := range points {
			tmp, _ := strconv.ParseFloat(v, 64)
			fpoints = append(fpoints, tmp)
		}
		a := (fpoints[1]-fpoints[3])/(fpoints[0]-fpoints[2])
		b := (fpoints[5]-fpoints[7])/(fpoints[4]-fpoints[6])
		if a == b {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

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

const double EPS = 1e-12;

double add(double a, double b) {
	if (abs(a + b) < EPS * (abs(a) + abs(b)))
		return 0;
	return a + b;
}

struct P {
	double x, y;
	P() {};
	P(double x, double y) : x(x), y(y) {
	}

	P operator + (P p) {
		return P(add(x, p.x), add(y, p.y));
	}

	P operator - (P p) {
		return P(add(x, -p.x), add(y, -p.y));
	}

	P operator * (double d) {
		return P(x * d, y * d);
	}

	P operator / (double d) {
		return P(x / d, y / d);
	}

	// 内積
	double dot(P p) {
		return add(x * p.x, y * p.y);
	}

	// 外積
	double det(P p) {
		return add(x * p.y, -y * p.x);
	}
};

// 線分上に点があるか
bool on_seg(P p1, P p2, P q) {
	return (p1 - q).det(p2 - q) == 0 && (p1 - q).dot(p2 - q) <= 0;
}

// 直線と直線の交点
P intersection(P p1, P p2, P q1, P q2) {
	return p1 + (p2 - p1) * ((q2 - q1).det(q1 - p1) / (q2 - q1).det(p2 - p1));
}

// 2直線の直行判定
bool line_orth(P a1, P a2, P b1, P b2) {
	return fabs((a1 - a2).dot(b1 - b2)) < EPS;
}

// 2直線の平行判定
bool line_paral(P a1, P a2, P b1, P b2) {
	return fabs((a1 - a2).det(b1 - b2)) < EPS;
}

int main(void) {
	int N;
	P p[4];
	cin >> N;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < 4; j++) {
			cin >> p[j].x >> p[j].y;
		}
		cout << (line_paral(p[0], p[1], p[2], p[3]) ? "YES" : "NO") << endl;
	}
}

C++: #include <cstdio>

using namespace std;

int main(void){
	int n, i;
	double x1,y1,x2,y2,x3,y3,x4,y4, vabx, vaby, vcdx, vcdy;
	scanf("%d",&n);
	for(i = 0;i < n;i++){
		scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		vabx = x1 - x2, vaby = y1 - y2;
		vcdx = x3 - x4, vcdy = y3 - y4;
		if((vabx == vcdx && vaby == vcdy) || (-vabx == vcdx && -vaby == vcdy)){
			printf("YES\n");
		}else{
			printf("NO\n");
		}
	}
	return 0;
}

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;
		}
	}


}