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>
#define rep(i,n) for(int i=0;i<(n);i++)
#define loop(i,x,n) for(int i=(x);i<(n);i++)
#define all(x) (x).begin(),(x).end()
#define pb push_back
#define mp make_pair
#define fir first
#define sec second
#define ub upper_bound
#define lb lower_bound
#define int long long
using namespace std;
const int MOD=1000000007;
const int INF=1000000009;


signed main(){
  int n;
  cin>>n;
  rep(i,n){
    double a,b,c,d,e,f,g,h;
    cin>>a>>b>>c>>d>>e>>f>>g>>h;
    if((b-d)*(e-g)==(f-h)*(a-c))cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
  return 0;
}

C++: #include<vector>
#include<iostream>
#include<cstdio>
using namespace std;
double x1,y1,x2,y2,x3,y3,x4,y4;
int n;
int main()
{
  scanf("%d\n",&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((y1-y2)/(x1-x2)==(y3-y4)/(x3-x4)){
	cout <<"YES"<<endl;
    }
    else
      cout<<"NO"<<endl;
  }
  return 0;
}

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

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

C++: #include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <algorithm>
#include <climits>
using namespace std;

int main(){
    double e = 1e-12;
    double x[4];
    double y[4];
    double s;
    double t;
    double u;
    double v;
    double m;
    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){
        double m = s * v - t * u;
    }
    else{
        double m = t * u - s * v;
    }

    if(m > e){
        cout << "YES" << endl;
    }
    else{
        cout << "NO" << endl;
    }
    return 0;
}

C++: #include <stdio.h>

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

	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);
		x2 = x2-x1;
		x4 = x4-x3;
		y2 = y2-y1;
		y4 = y4-y3;

		if((y2 != 0 && y4 != 0 && x2/y2 == x4/y4) || (y2 == 0 && y4 == 0)) printf("YES\n");
		else printf("NO\n");
	}

	return 0;
}

C++: #include<iostream>
using namespace std;
int main(){
  int n;
  double x[4],y[4],bell1,hess1,bell2,hess2;
  cin >> n;
  for(int t=0;t<n;t++){
    for(int i=0;i<4;i++){
      cin >> x[i] >> y[i];
    }
    bell1=x[0]-x[1];
    hess1=y[0]-y[1];
    bell2=x[2]-x[3];
    hess2=y[2]-y[3];
    if(bell1==bell2 && hess1==hess2){
      cout << "YES" << endl;
    }
    else{
      cout << "NO" << endl;
    }
  }
}

C++: #include<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main() {
	int n;
	cin >> n;
	for (int z = 0; z < n; z++) {
		long float x1, x2, x3,y1, y2, y3, y4, x4 ;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (y1 > y2) {
			swap(y1, y2);
			swap(x1, x2);
		}
		if (y3 > y4) {
			swap(y3, y4);
			swap(x3, x4);
		}
		if ((x1 > x2&&x3 > x4 && ((y2 - y1) / (x1 - x2) == (y4 - y3) / (x3 - x4))) || (x2 > x1&&x4 > x3 && ((y1 - y2) / (x2 - x1) == (y3 - y4) / (x4 - x3)))) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}

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

C++: #include<iostream>

using namespace std;

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;
		cout << ((((y2 - y1) / (x2 - x1)) == ((y4 - y3) / (x4 - x3))) ? "YES\n" : "NO\n");
	}

	return 0;
}

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

int main(){
  int n;
  cin >> n;

  for(int i=0;i<n;i++){
    complex<double> v[4];
    for(int j=0;j<4;j++){
      double x,y;
      cin >> x >> y;
      v[j]=complex<double>(x,y);
    }

    if((conj(v[1]-v[0])*(v[3]-v[2])).imag()==0)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <cmath>
using namespace std;
int main(){
  

  int dataSets;
  cin >> dataSets;
  for(int i=0;i<dataSets;i++){
    double x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if(abs((y2-y1)*(x4-x3) - (x2-x1)*(y4-y3)) < 0.0001){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
    
  }

  return 0;

}

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

#define EPS (1e-10)

int main(){
    int n;
    double x1,x2,x3,x4,y1,y2,y3,y4;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
 
 
        double a,b;
        a=(y2-y1)/(x2-x1);
        b=(y4-y3)/(x4-x3);
        (fabs(a-b)<=EPS)? cout<<"YES"<<endl : cout<<"NO"<<endl;
    }
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
using ll = long long;
using vi = vector<int>;
using vii = vector<vector<int>>;
using vl = vector<ll>;
using vll = vector<vector<ll>>;
using pii = pair<int,int>;
#define FOR(i,a,b) for(ll i = (a); i < (b); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(obj) (obj).begin(), (obj).end()
#define pb push_back
#define double long double
const double pi = acos(-1);
const double EPS = 1e-10;

double crosss(pair<double,double> c,pair<double,double> d){
  return c.first * d.second - d.first * c.second;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  vector<pair<double,double>> a(4);
  int n;
  pair<double,double> lineab, linecd;
  cin >> n;
  REP(i,n){
    REP(j,4){
      cin >> a[j].first >> a[j].second;
    }
    lineab.first = a[1].first - a[0].first;
    linecd.first = a[3].first - a[2].first;
    lineab.second = a[1].second - a[0].second;
    linecd.second = a[3].second - a[2].second;
    if (fabs(crosss(lineab,linecd)) == 0){
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  
  
  return 0;
}

C++: #include <iostream>

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 a = x2 - x1, b = y2 - y1, c = x4 - x3, d = y4 - y3;
    if (a * d - b * c == 0.0)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}

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

int main(){
	double x1,x2,x3,x4,y1,y2,y3,y4,a,b;
	int n,i;
	
	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);
		
		a=(y1-y2)/(x1-x2);
        b=(y3-y4)/(x3-x4);
        if(a==b)printf("YES\n");
        else printf("NO\n");
	}	
return 0;
}