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 <bits/stdc++.h>
using namespace std;
#define FOR(i, s, n) for(int i = s; i < (int)n; i++)
#define per(i, n) for(int i = n; i >= 0; i--)
#define ROF(i, s, n) for(int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\n"
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n) for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define CLR(a) memset((a), 0 ,sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\n";
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << "\n";
#define sq(n) (n) * (n)
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue< int, vector<int>, greater<int> > minpq;
static const double EPS = 1e-10;
static const double PI = acos( -1.0 );
static const int mod = 10007;
static const int INF = 1 << 25;
static const LL LL_INF = 1152921504606846976;
static const int dx[] = { -1, 0, 1, 0,  1, -1,  1, -1 };
static const int dy[] = { 0, -1, 0, 1 , 1,  1, -1, -1 };

int n;
double x1, x2, x3, x4, y1, y2, y3, y4;

int main() {
	scanf( "%d", &n );
	for ( int i = 0; i < n; i++ ) {
		scanf( "%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4 );
		if ( fabs( ( x2 - x1 ) * ( y4 - y3 ) - ( x4 - x3 ) * ( y2 - y1 ) ) < EPS ) {
			printf( "YES\n" );
		}
		else {
			printf( "NO\n" );
		}
	}
	return 0;
}

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

using namespace std;

int main() {
	int k;
	double x1,x2,x3,x4,y1,y2,y3,y4;
	double veku1[2];
	double veku2[2];
	double veku3[2];
	double veku4[2];
	double t;

	cin >> k;

	for (int i = 0; i < k; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		veku1[0] = x2 - x1;
		veku1[1] = y2 - y1;
		veku2[0] = x4 - x3;
		veku2[1] = y4 - y3;

		t = veku1[0] * veku2[0] + veku1[1] * veku2[1];

		if (t * t != (veku1[0] * veku1[0] + veku1[1] * veku1[1]) * (veku2[0] * veku2[0] + veku2[1] * veku2[1])) {
			cout << "NO" << endl;
		} else {
			veku3[0] = x3 - x1;
			veku3[1] = y3 - y1;
			veku4[0] = x4 - x1;
			veku4[1] = y4 - y1;

			t = veku3[0] * veku4[0] + veku3[1] * veku4[1];

			if (t * t != (veku3[0] * veku3[0] + veku3[1] * veku3[1]) * (veku4[0] * veku4[0] + veku4[1] * veku4[1])) {
				cout << "YES" << endl;
			} else {
				cout << "NO" << endl;
			}
		}
	}
	return 0;
}

C++: #include<iostream>
#include<math.h>
#include<stdio.h>
using namespace std;
int n,AB,CD;
double ax,ay,bx,by,cx,cy,dx,dy,ab,cd,abx,aby,cdx,cdy;
int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		AB=CD=0;
		cin>>ax>>ay>>bx>>by>>cx>>cy>>dx>>dy;
		abx=(ax-bx);
		cdy=(cy-dy);
		aby=(ay-by);
		cdx=(cx-dx);
		if(abx==0.0)AB=1;
		if(aby==0.0)AB=2;
		if(cdx==0.0)CD=1;
		if(cdy==0.0)CD=2;
		if(abx*cdy==cdx*aby&&AB==CD)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
int main()
{
	long double x1,y1,x2,y2,x3,y3,x4,y4;
	int n;
	cin>>n;
	int N[100];
for(int i=0;i<n;i++)
{
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
	if((y1-y2)/(x1-x2)==(y3-y4)/(x3-x4))
	{
	N[i]=1;
	}
	else
	{
	N[i]=0;
	}
}
for(int j=0;j<n;j++)
{
	if(N[j]=1)
	{
		cout<<"YES"<<endl;
	}
	else if(N[j]=0)
	{
		cout<<"NO"<<endl;
	}
}
return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <string>
#include <math.h>
#include <algorithm>
#include <vector>

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;
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		//cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		
		if((x2 - x1)*(y4 - y3) != (x4 - x3)*(y2 - y1)){
			cout << "NO" << endl;
		}
		else{
			cout << "YES" << endl;
		}

	}
	return 0;
}

C++: #include <cstdio>
#include <cmath>

using namespace std;

int main(void){
	int n, i;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	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);
		if(((y2 - y1) * (x4 - x3)) == ((x2 - x1) * (y4 - y3))){
			printf("YES\n");
		}else{
			printf("NO\n");
		}
	}
	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, x2, x3, x4, y1, y2, y3, y4, a, b;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    a = (y2 - y1) / (x2 - x1);
    b = (y4 - y3) / (x4 - x3);
    if (a == b) cout << "YES\n";
    else cout << "NO\n";
  }
}

C++: #include <cassert>
#include <cmath>
#include <iostream>
#include <vector>
#include <iomanip>

struct Point
{
    double x;
    double y;
};
struct Line
{
    Line(const Point& a, const Point& b)
    : p1(a), p2(b) {}
    Point p1;
    Point p2;
};
double GetSlope(const Line& line)
{
    return
    (line.p2.y - line.p1.y) /
    (line.p2.x - line.p1.x);
}
bool IsParallel(const Line& l1, const Line&l2)
{
    // std::cerr << std::fixed << std::setprecision(100) << GetSlope(l1) << std::endl;
    // std::cerr << std::fixed << std::setprecision(100) << GetSlope(l2) << std::endl;
    return GetSlope(l1) == GetSlope(l2);
    // const double gosa = 1e-10;
    // double Slope1 = GetSlope(l1);
    // double Slope2 = GetSlope(l2);
    // return std::fabs(Slope1 - Slope2) < gosa;
}
bool IsParallel(const std::vector<Point>& points)
{
    assert(points.size() == 4);
    return IsParallel(Line(points[0], points[1]), Line(points[2], points[3]));
}
std::vector<Point> Input(std::istream& is)
{
    std::vector<Point> points(4);
    for(int i = 0; i < points.size(); ++i){
        is >> points[i].x >> points[i].y;
    }
    return points;
}
int main()
{
    int n;
    std::cin >> n;
    for(int i = 0; i < n; ++i) {
        std::vector<Point> points = Input(std::cin);
        std::cout << (IsParallel(points) ? "YES" : "NO") << std::endl; 
    }
    return 0;
}