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

#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for (int i = x; i < n; i++)
#define OP(m) cout << m << endl;
typedef long long ll;
typedef unsigned long long ull;

int main()
{
    double x1, x2, x3, x4, y1, y2, y3, y4;
    int n;
    cin >> n;
    rep(i, n)
    {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        if (abs((y2 - y1) * (x4 - x3) - (y4 - y3) * (x2 - x1)) < 0.0000000001)
        {
            OP("YES")
        }
        else
        {
            OP("NO")
        }
    }
    return 0;
}

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

struct Vector2D {
	double x;
	double y;

	Vector2D& operator-=(const Vector2D& rhs) {
		x -= rhs.x;
		y -= rhs.y;
		return *this;
	}
};

Vector2D operator-(const Vector2D& lhs, const Vector2D& rhs)
{
	return Vector2D(lhs) -= rhs;
}

int main()
{
	int count = 0;
	std::cin >> count;
	for (int i = 0; i < count; ++i) {
		Vector2D pA, pB, pC, pD;
		std::cin >> pA.x >> pA.y >> pB.x >> pB.y >> pC.x >> pC.y >> pD.x >> pD.y;

		Vector2D rAB(pB - pA), rCD(pD - pC);
		if (rAB.x * rCD.y - rAB.y * rCD.x < 1.0e-6) {
			std::cout << "YES\n";
		} else {
			std::cout << "NO\n";
		}
	}

	return 0;
}

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

int main() {
float x1,x2,x3,x4,y1,y2,y3,y4;
int n;
cin>>n;
for(int jjj=1;jjj<=n;jjj++){
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
	if(x1==x2||x3==x4){
		if(x3==x4&&x1==x2){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}}
	else{
		double k=(y2-y1)/(x2-x1),l=(y4-y3)/(x4-x3);
		if(k==l){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}
	}	
	}

	return 0;
}

C++: #include <iostream>
#include <math.h>

using namespace std;

int main(void){
	int n, i;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	double dega, degb;

	cin >> n;

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

		dega = (y2 - y1) / (x2 - x1);
		degb = (y4 - y3) / (x4 - x3);
	
		if(fabs(dega - degb) < 1.0e-6){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		}
	}

	return 0;
}

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

int main() {
	int n;
	double x1, x2, x3, x4, y1, y2, y3, y4;
	vector<double> X1, Y1, X2, Y2;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		X1.push_back(x2 - x1); Y1.push_back(y2 - y1);
		X2.push_back(x4 - x3); Y2.push_back(y4 - y3);
	}
	for (int i = 0; i < n; i++) {
		double det = fabs(X1[i] * Y2[i] - X2[i] * Y1[i]);
		if (fabs(det)<1e-10)cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include<stdio.h>

int main(void)
{
	double x[4]={0},y[4]={0},x1,x2,y1,y2;
	int i;
	scanf("%d",&i);

	while(i!=0)
	{
		scanf("%f %f %f %f %f %f %f %f",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2],&x[3],&y[3]);
		if(x[1]-x[0] == 0 && x[3]-x[2] == 0)
			printf("YES\n");
		else if(x[1]-x[0] == 0 || x[3]-x[2] == 0)
			printf("NO\n");
		else if((y[1]-y[0])/(x[1]-x[0]) == (y[3]-y[2])/(x[3]-x[2]))
			printf("YES\n");
		else 
			printf("NO\n");

		i-=1;
	}
 return 0;
}

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

using namespace std;
typedef long long ll;

typedef long double R;
typedef complex<R> P;

const R EPS = 1e-13;
const R PI = acos(-1);
int sgn(R a) {
    if (a < -EPS) return -1;
    if (a > EPS) return 1;
    return 0;
}


bool near(P a, P b) {
    return !sgn(abs(a-b));
}

void solve() {
    P p[4];
    for (int i = 0; i < 4; i++) {
        long double x, y;
        cin >> x >> y;
        p[i] = P(x, y);
    }
    long double r1 = arg(p[1]-p[0]);
    long double r2 = arg(p[3]-p[2]);
    if (r1 < 0) r1 += PI;
    if (r2 < 0) r2 += PI;
    if (sgn(r1-r2)) {
        cout << "NO" << endl;
    } else {
        cout << "YES" << endl;
    }
}

int main() {
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        solve();
    }
    return 0;
}