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 EPS = 1e-12;
    double x[4], y[4];
    int s,t,u,v;
    int n;
    cin >> n;
    for (int t = 0;t < n;++t) {
        for (int i = 0;i < 4;++i){
            cin >> x[i] >> y[i]; 
        }
    }
    s = x[1] - x[0];
    t = y[1] - y[0];
    u = x[3] - x[2];
    v = y[3] - y[2];
    if(s * v - t * u > 0){
        int m = s * v - t * u;
    }
    else{
        int m = t * u - s * v;
    }
    if( m < eps){
        cout << "YES" << endl;
    }
    else{
        cout << "NO" << endl;
    }
    return 0;
}

C++: #include <map>
#include <set>
#include <stack>
#include <queue>
#include <cmath>
#include <string>
#include <vector>
#include <iostream>
#include <algorithm>

using namespace std;

#define endl '\n'

typedef long long ll;
typedef long double lb;
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;}

const ll MOD = 1e9 + 7;
const ll INF = 1e9 + 9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1};
const int dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

int main()
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  
  double x1, y1, x2, y2, x3, y3, x4, y4;
  int n;
  cin >> n;
  for (int i = 0; i < n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    double s1 = (y2 - y1) / (x2 - x1), s2 = (y4 - y3) / (x4 - x3);

    if (s1 == s2) cout << "YES" << endl;

    //if ((x1 == x2 && x3 == x4) || (((y2 - y1) / (x2 - x1)) == ((y4 - y3) / (x4 - x3)))) cout << "YES" << endl;

    else cout << "NO" << endl;
  }
  return (0);
}

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

using namespace std;

void myswap(double* a,double* b)
{
	double temp=*a;
	*a=*b;
	*b=temp;
}
int main()
{
	double x1,x2,x3,y1,y2,y3,x4,y4;
	int n;
	double AB,CD; 

	cin>>n;

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

		if(x2==x1||x4==x3)
		{
			if(x2==x1&&x4==x3)
			{
				cout<<"YES"<<endl;
			}
			else
			{
				cout<<"NO"<<endl;
			}
			continue;
		}
		
		AB=(y2-y1)/(x2-x1);
		CD=(y4-y3)/(x4-x3);
		if(AB<CD)
		{
			myswap(&AB,&CD);
		}

		if((AB-CD)<0.001)
		{
			cout<<"YES"<<endl;
		}
		else
		{
			cout<<"NO"<<endl;
		}

	}
	

	return 0;
}

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

using namespace std;

typedef struct myvector{
  double x;
  double y;
}Vector;

Vector sub_vector(Vector& a, Vector& b)
{
  Vector ret;
  ret.x = b.x - a.x;
  ret.y = b.y - a.y;
  return ret;
}

double cross_product(Vector& a, Vector& b)
{
  return a.x * b.y - b.x * a.y;
}

int main()
{
  int n;
  cin >> n;
  for(int i = 0; i < n; i++){
    Vector A, B, C, D;
    cin >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y >> D.x >> D.y;
    Vector AB = sub_vector(A, B);
    Vector CD = sub_vector(C, D);
    if(fabs(cross_product(AB, CD)) < 1.0e-10)
      cout << "YES" << endl;
    else 
      cout << "NO" << endl;
  }
}

C++: #include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long long ll;
const int maxn=10000000;
bool is_prime[maxn];
int solve1(int n){
	for(int i=0;i<=n;i++)is_prime[i]=true;
	int ans=0;
	for(int i=2;i<=n;i++){
		if(is_prime[i]){
			ans++;
			for(int j=i*2;j<=n;j+=i)is_prime[j]=false;
		}
	}
	return ans;
}



int main(){
	int n;
	cin>>n;
	double x1,y1,x2,y2,x3,y3,x4,y4;
	while(n--){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double t1=abs(y2-y1);
		double t2=abs(x2-x1);
		double t3=abs(y4-y3);
		double t4=abs(x4-x3);
		if(t1/t2==t3/t4)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<vector>
#include<utility>
#include<queue>
#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<complex>
#define INF 1e9
#define llINF 9223372036854775807
#define pb push_back
#define mp make_pair 
#define F first
#define S second
#define ll long long

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;
    if((abs(y1-y2)/abs(x1-x2))==(abs(y3-y4)/abs(x3-x4)))
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int main(){
  int n;
  double x1,x2,x3,x4,y1,y2,y3,y4;
  cin >> n;
  string ans[n];
  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) and (y1-y3)/(x1-x3)!=(y1-y2)/(x1-x2) and (y1-y4)/(x1-x4)!=(y1-y2)/(x1-x2) x1-x2!=0 and x3-x4!=0 and y1-y2!=0 and y3-y4!=0){
      ans[i]="YES";
    }else{
      ans[i]="NO";
    }
  }
  for(int i=0;i<n;i++){
    cout << ans[i] << endl;
  }
  return 0;
}

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

int main()
{
	int n;
	double p[4][2];
	
	cin >> n;

	for (int x = 0; x < n; ++x){
		for (int i = 0; i < 4; ++i){
			for (int j = 0; j < 2; ++j){
				cin >> p[i][j];
			}
		}

		if ((p[0][0] - p[1][0]) / (p[0][1] - p[1][1]) == (p[2][0] - p[3][0]) / (p[2][1] - p[3][1]))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}

C++: import java.io.*;

class Main{
public static void main(String[] args) throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String line=br.readLine();
int n = Integer.parseInt(line);
for (int i = 0; i < n; i++) {
String line = br.readLine();
String[] values = line.split(" ");
double x1 = Double.parseDouble(values[0]);
double y1 = Double.parseDouble(values[1]);
double x2 = Double.parseDouble(values[2]);
double y2 = Double.parseDouble(values[3]);
double x3 = Double.parseDouble(values[4]);
double y3 = Double.parseDouble(values[5]);
double x4 = Double.parseDouble(values[6]);
double y4 = Double.parseDouble(values[7]);
System.out.println((x2 - x1) * (y4 - y3) == (y2 - y1) * (x4 - x3) ? "YES" : "NO");
}
}
}

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

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

	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (fabs((y2 - y1) * (x4 - x3) - (y4 - y3) * (x2 - x1)) < 0.0000000001) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}