Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextInt() int {
	scanner.Scan()
	i, e := strconv.Atoi(scanner.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func main() {
	n := nextInt()
	for i := 0; i < n; i++ {
		scanner.Scan()
		points := strings.Split(scanner.Text(), " ")
		fpoints := make([]float64, 0)
		for _, v := range points {
			tmp, _ := strconv.ParseFloat(v, 64)
			fpoints = append(fpoints, tmp)
		}
		if fpoints[0] == fpoints[2] && fpoints[4] == fpoints[6] {
			fmt.Println("YES")
		} else {
			a := (fpoints[1] - fpoints[3]) / (fpoints[0] - fpoints[2])
			b := (fpoints[5] - fpoints[7]) / (fpoints[4] - fpoints[6])
			if a == b {
				fmt.Println("YES")
			} else {
				fmt.Println("NO")
			}
		}
	}
}

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

int main(){
	int n;
	cin >> n;
	while(n-->0){
		double x1,x2,x3,x4,y1,y2,y3,y4;
		cin >>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double xa = x2-x1;
		double xb = x4-x3;
		double ya = y2-y1;
		double yb = y4-y3;
		if(abs(xa*yb-xb*ya)<0.0000000001) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}

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

int main()
{
    int n;
    cin>>n;
    while(n--){
        pair<double,double>a[4];
        for(int i=0;i<4;i++){
            cin>>a[i].first>>a[i].second;
        }
       if(((a[1].second-a[0].second)*(a[3].first-a[2].first))!=((a[3].second-a[2].second)*(a[1].first-a[0].first)))
            cout<<"NO"<<endl;
        else
            cout<<"YES"<<endl;
    }
    return 0;
}

C++: #include<iostream>
using namespace std;
int main(){
  double a[2],b[2],c[2],d[2];
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    for(int j=0;j<2;j++) cin >> a[j] >> b[j] >> c[j] >> d[j];
    if(a[0]-b[0]==0&&c[0]-d[0]==0) cout << "YES" << endl;
    else if(a[1]-b[1]==0&&c[1]-d[1]==0) cout << "YES" << endl;
    if(a[0]-b[0]!=0&&c[0]-d[0]!=0){
    if((a[1]-b[1])/(a[0]-b[0])==(c[1]-d[1])/(c[0]-d[0])) cout << "YES" << endl;
    }
    else cout << "NO" << endl;
  }   
  return 0;
}

C++: #include<iostream>
using namespace std;
 
int main(void){
  double xa,ya,xb,yb,xc,yc,xd,yd;
  int n;
  cin >> n;
  while( --n >=0){
    cin >> xa >> ya >> xb >> yb >> xc >> yc >> xd >> yd;
 
    if( (yb - ya)/(xb - xa) == (yd - yc)/(xd - xc))
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }
  return 0;
}

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

const double EPS = 1E-5;

inline bool cmp(double x, double y){
  return abs(x-y) < EPS;
}

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

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

int main()
{
	char dust;
	int n, i, j;
	double x[4], y[4];

	cin >> n;

	for (i = 0; i < n; i++)
	{
		for (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 <iostream>

int main(){
	
	double a,x1,y1,x2,y2,x3,y3,x4,y4;
	std::cin>>a;
	for(int s=0;s<a;s++){
		std::cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		if((y2-y1)/(x2-x1)==(y4-y3)/(x4-x3)||(y2-y1)/(x2-x1)==-1/((y4-y3)/(x4-x3))){
			std::cout<<"YES"<<std::endl;
		}else{
			std::cout<<"NO"<<std::endl;
		}
		
    }
    return 0;
}

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

typedef double Real;
typedef complex<Real> Point;
typedef pair<Point,Point> Line;

const Real EPS=1e-10;


inline Point vec(const Line& a){
    return a.second-a.first;
}

Real dot(Point a,Point b){
    return (conj(a)*b).real();
}

Real cross(Point a,Point b){
    return (conj(a)*b).imag();
}

inline int sgn(Real a,Real b=0){
    return a < b - EPS ? -1 : a > b + EPS ? 1 : 0;
}

inline bool near(Point a,Point b){
    return !sgn(abs(a-b));
}

inline bool is_orthogonal(Line la,Line lb){
    return !sgn(dot(vec(la),vec(lb)));
}

inline bool is_parallel(Line la,Line lb){
    return !sgn(cross(vec(la),vec(lb)));
}

inline bool is_intersected_line(Line la,Line lb){
    return !is_parallel(la,lb);
}

inline Real arg(const Point& base,const Point& a,const Point& b){
    return arg((b-base)/(a-base));
}

inline Real sr(Real a){
    return sqrt(max(a,(Real)0));
}

inline Real dist(Point a,Point b){
    return abs(a-b);
}

inline Real length(Point a){
    return abs(a);
}

inline Point unit_vector(Point a){
    return a / abs(a);
}


Point rotate(Point x,Real rad){
    return Point(x.real()*cos(rad)-x.imag()*sin(rad),x.real()*sin(rad)+x.imag()*cos(rad));
}                             



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

    int n;
    Point A[4];

    cin>>n;
    for(int i=0;i<n;i++){
        for(auto &t:A){
            double x,y;
            cin>>x>>y;
            t=Point(x,y);
        }

        Line la=make_pair(A[0],A[1]),lb=make_pair(A[2],A[3]);

        cout << (is_parallel(la,lb) ? "YES" : "NO") << endl;
    }

    return 0;
}

C++: #include<iostream>
#include<cmath>
#include<cassert>
#include<cstdlib>
using namespace std;
#define EPS 0.000001


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

  
      if ( abs((y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1) ) < EPS ) cout << "YES" << endl;
      else cout << "NO" << endl;
  }
}

C++: #include <iostream>


using namespace std;

int main()
{
	int i,num;
	float x[4],y[4];
	cin >> num;

	for ( i = 0 ; i< num; i++ ) {
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

		if( (x[0]-x[1])*(y[2]-y[3]) == (y[0]-y[1])*(x[2]-x[3]) ){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
	return 0;
}

C++: #include <iostream>

using namespace std;
 
double kata(double x, double y, double xx, double yy)
{
    return (yy-y)/(xx-x);
}
 
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(kata(x1,y1,x2,y2)==kata(x3,y3,x4,y4))
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }

    return 0;

}

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

#define iota(i,n,b,s) for(int i=int(b);i!=int((b)+(s)*(n));i+=(s))
#define range(i,n,m) iota(i,(((n)>(m))?((n)-(m)+1):((m)-(n)+1)),(n),((n)>(m)?-1:1))
#define rep(i,n) iota(i,(n),0,1)

#define INF (1e9)
#define EPS (1e-9)
#define cons(a,b) (make_pair(a,b))
#define car(a) (a.first)
#define cdr(a) (a.second)
#define cadr(a) (car(cdr(a)))
#define cddr(a) (cdr(cdr(a)))
#define all(a) a.begin(), a.end()
#define trace(var) cerr<<">>> "<<#var<<" = "<<var<<endl;

typedef long long Integer;
typedef double Real;

template<class S, class T>
ostream& operator<<(ostream& os, pair<S,T> p) {
  os << '(' << car(p) << ", " << cdr(p) << ')';
  return os;
}

template<class T>
ostream& operator<<(ostream& os, vector<T> v) {
  os << v[0];
  for (int i=1, len=v.size(); i<len; ++i) os << ' ' << v[i];
  return os;
}

int dx[] = { -1, 0, 1, 0 };
int dy[] = {  0, -1, 0, 1 };

int main() {

  int n; cin >> n;

  while (n--) {

    Real x1,y1,x2,y2,x3,y3,x4,y4;
    cin >> x1 >> y1 >> x2 >> y2;
    cin >> x3 >> y3 >> x4 >> y4;

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

    if (abs(x1 * y3 - y1 * x3) < 1e-5) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }

  }

  return 0;
}

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

int main() {
	long double x1, y1, x2, y2, x3, y3, x4, y4;
	int n; cin >> n;
	for (; n > 0; n--) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if ((x1-x2)*(y3-y4) == (y1-y2) * (x3-x4))
			cout << "YES\n";
		else
			cout << "NO\n";
	}
	return 0;
}