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 <bits/stdc++.h>
/* Karen {{{
  ___  ____
 |_  ||_  _|
   | |_/ /    ,--.   _ .--.  .---.  _ .--.
   |  __'.   `'_\ : [ `/'`\]/ /__\\[ `.-. |
  _| |  \ \_ // | |, | |    | \__., | | | |
 |____||____|\'-;__/[___]    '.__.'[___||__]
}}} */
/* cpp template {{{*/
using namespace std;

#define endl '\n'

#define REP(i, n) for (int i = 0; i < (n); i++)
#define REPS(i, a, n) for (int i = (a); i < (n); i++)
#define RREP(i, n) for (int i = 1; i <= (n); i++)
#define X real()
#define Y imag()
#define EQ(n,m) (abs((n)-(m)) < EPS)

typedef double D;
typedef long long ll;
typedef long double lb;
typedef complex<D> P;
typedef vector<P> VP;
typedef vector<int> vi;
typedef vector<vector<int> > vii;
typedef pair<int, int> pii;
typedef pair<int, string> pis;
typedef pair<string, int> psi;

inline bool inside(int y,int x,int H,int W){return(y>=0&&x>=0&&y<H&&x<W);}
inline int in() {int x; std::cin >> x; return x;}

template <typename T>
void print(std::vector<T>& v, char c = ' ') {
  REP(i, v.size()) {
    if (i != 0) std::cout << c;
    std::cout << v[i];
  }
  std::cout << endl;
}
template <typename T>
void print(T x) {
  std::cout << x << '\n';
}
/* }}} */
/* ?????° {{{*/
const ll MOD = 1e9 + 7;
const ll INF = 1e9 + 9;
const D EPS  = 1e-5;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1};
const int dy[] = {1, 0, -1, 0, 1, -1, -1, 1};
/* }}} */

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

  int n = in();
  float x[4], y[4];

  while(n--){
    REP(i, 4) cin >> x[i] >> y[i];
    float l1, l2;
    l1 = (y[1] - y[0]) / (x[1] - x[0]);
    l2 = (y[3] - y[2]) / (x[3] - x[2]);
    if ((l1 - l2) < EPS * l1){
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  return (0);
}

C++: #include <iostream>
#include <cmath>
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;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        double m1 = (y1-y2)/(x1-x2);
        double m2 = (y3-y4)/(x3-x4);
        cout << (m1 == m2 ? "YES" : "NO") << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<math.h>
#include<string>
#include<vector>
#include<algorithm>
#include<queue>
#include<map>
using namespace std;
#define INF 1<<20

struct edge{
	int to;
	int cost;
	edge() {};
	edge(int a, int b) {
		to = a;
		cost = b;
	}
};

struct Node {
	int pos;
	int cost;
	Node() {};
	Node(int a, int b) {
		pos = a;
		cost = b;
	}
	bool operator <(const Node& rhs) const {
		return cost > rhs.cost;
	}
};

void dijkistra(int st, int TO,int V,vector<vector<edge> > graph) {
	priority_queue<Node> q;
	vector<int> d(V);
	for (int i = 0;i < V;i++) {
		d[i] = INF;
	}
	d[st] = 0;
	q.push(Node(st, 0));
	while (!q.empty()) {
		Node s = q.top(); q.pop();
		int pos = s.pos;
		for (int i = 0;i < graph[pos].size();i++) {
			int to = graph[pos][i].to;
			int cost = graph[pos][i].cost;
			if (d[pos] + cost < d[to]) {
				d[to] = d[pos] + cost;
				q.push(Node(to, d[to]));
			}

		}
	}
	cout << d[TO] << endl;
}
int partition(int A[],int p, int r) {
	int x = A[r];
	int i = p - 1;
	for (int j = p;j < r;j++) {
		if (x >= A[j]) {
			i = i + 1;
			swap(A[i], A[j]);
		}
	}
		swap(A[i + 1], A[r]);
		return i + 1;
}
void quicksort(int A[], int p, int r) {
	if (p < r) {
		int q = partition(A, p, r);
		quicksort(A, p, q-1);
		quicksort(A, q + 1, r);
	}
}

int getNumberOfCoin(int C[],int n,int m) {
	int T[50000];
	for (int j = 0;j <= n;j++) {
		T[j] = INF;
	}
	T[0] = 0;
	for (int i = 0;i < m;i++) {
		for (int j = 0;j <= n;j++) {
			if (j - C[i] >=0  ) {
				T[j] = min(T[j], T[j - C[i]] + 1);
			}
		}
	}
	return T[n];
}
int knapsack(int w, int n,int* v,int* ww) {
	int W[101][10001];
		for (int j = 0;j <= w;j++) {
			W[0][j] = 0;
		}
	for (int i = 0;i < n;i++) {
		for (int k = 0;k < n;k++){
			for (int j = 0;j <= w;j++) {
				if (j - ww[k] < 0) {
					W[i + 1][j] = W[i][j];
				}
				if (j - ww[i] >= 0) {
					W[i + 1][j] = max(W[i][j], W[i][j - ww[k]] + v[k]);

				}
			}
		}
	}
	return W[n][w];
}
int fib(int n) {
	vector<int> v(n+1);
	v[0] = 1;
	v[1] = 1;
	for (int i = 2;i < n+1;i++) {
		v[i] = v[i - 2] + v[i - 1];
	}
	return v[n];
}
int isPrime(int x) {
	if (x <= 1) return false;
	if (x>2 && x % 2 == 0) return false;
	for (int i = 2;i <= sqrt(x);i++) {
		if (x%i == 0) {
			return false;
		}
	}
	if (x == 2) return true;
	return true;
}
int Prime(int x) {
	vector<int> prime(x+1,1);
	int num = 2;
	while (num <= sqrt(x)) {
		for (int i = 2;i <= x / num;i++) {
			prime[num*i] = 0;
		}
		num++;
		while (prime[num] == 0)
			num++;
	}
	int count = 0;
	for (int i = 2;i < x + 1;i++) {
		if (prime[i] == 1) count++;
	}
	return count;
}
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 X1 = x[1] - x[0];
		double Y1 = y[1] - y[0];
		double X2 = x[3] - x[2];
		double Y2 = y[3] - y[2];
		if (X1*Y2 == X2*Y1) cout << "YES"<<endl;
		else cout << "NO"<<endl;
	}
	

}

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

int main(){

  int n;
  double x[4], y[4];

  cin>>n;
  for(int i=0;i<n;i++){
    for(int j=0;j<4;j++) cin>>x[j]>>y[j];
    if((x[1]-x[0])/(y[1]-y[0])==(x[3]-x[2])/(y[3]-y[2])) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }

  return 0;
}

C++: #include <stdio.h>

int main(){
    int n;
    double x1, y1, x2, y2;
    double x3, y3, x4, y4;
    double dx1, dy1, dx2, dy2;
    
    scanf("%d", &n);
    for (int i=0; i<n; i++){
        scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
        scanf("%lf %lf %lf %lf", &x3, &y3, &x4, &y4);
        dx1 = x2 - x1;
        dy1 = y2 - y1;
        dx2 = x4 - x3;
        dy2 = y4 - y3;
        if (dx1*dy2 == dx2*dy1){
            printf("YES\n");
        } else {
            printf("NO\n");
        }
    }

    return 0;
}

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