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<iostream>
using namespace std;

int main(){
	double x[4], y[4];
	int n;
	cin >> n;
	for( int i=0; i<n; i++ ){
		for( int j=0; j<4; j++ )
			cin >> x[j] >> y[j];
		double ab = (y[1]-y[0])/(x[1]-x[0]);
		double cd = (y[3]-y[2])/(x[3]-x[2]);
		cout << (ab==cd?"YES":"NO") << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstdlib>
#include <cstring>

using namespace std;

#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define REP(i,n) FOR(i,0,n)

typedef long long ll;

int main(){
	int n;
	
	cin >> n;
	
	while (n--){
		double x1, x2, x3, x4;
		double y1, y2, y3, y4;
		
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
		
		double dx12, dy12, dx34, dy34;
		double a12, a34;
		
		if (x1 < x2){
			dx12 = x2 - x1;
			dy12 = y2 - y1;
		}
		else {
			dx12 = x1 - x2;
			dy12 = y1 - y2;
		}
		
		if (x3 < x4){
			dx34 = x4 - x3;
			dy34 = y4 - y3;
		}
		else {
			dx34 = x3 - x4;
			dy34 = y3 - y4;
		}
		
		a12 = dy12/dx12;
		a34 = dy34/dx34;
		
		if (a12 == a34) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	
	return 0;
}

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

int main(){

	typedef struct{
		double x, y;
	}_td;

	int n;
	_td p1, p2, p3, p4, v_ab, v_cd;
	double del, eps;
	eps = 0.000001;
	
	cin >> n;
	
	for(int i=0; i<n; i++){
		cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y >> p4.x >> p4.y;
	
		v_ab.x = p2.x - p1.x;
		v_ab.y = p2.y - p1.y;
		v_cd.x = p4.x - p3.y;
		v_cd.y = p4.x - p3.y;
		
		del = v_ab.x * v_cd.y - v_ab.y * v_cd.x;
		if(abs(del) < eps) cout << "YES" << endl;
		else cout << "NO" << endl;
	}

	return 0;

}

C++: #include <iostream>
 
using namespace std;
 
int main(){
    int n;
    double x[100],y[100];
    cin>>n;
    while(n>0){
        for(int i=0;i<4;i++)cin>>x[i]>>y[i];
        if((y[0]-y[1])/(x[0]-x[1])==(y[2]-y[3])/(x[2]-x[3])){
            cout<<"YES"<<endl;
            n--;
        }
        else {
            cout<<"NO"<<endl;
            n--;
        }
    }
}