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)
		}
		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 <bits/stdc++.h>
using namespace std;
using ld = long double;
const ld eps = 1e-11;

int main()
{
	int n;
	ld x1, x2, x3, x4, y1, y2, y3, y4;
	cin >> n;
	while (n--) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		ld dx1 = x2 - x1, dy1 = y2 - y1;
		ld dx2 = x4 - x3, dy2 = y4 - y3;
		if (abs(dx1 * dy2 - dy1 * dx2) < eps && dx1 * dx2 + dy1 * dy2 > -eps) {
			puts("YES");
		}
		else {
			puts("NO");
		}
	}
	return 0;
}

C++: #include<iostream>
#include<cmath>
#define EPS 0.000000000001
using namespace std;

int main(){
	int n;
	double x[4], y[4];
	cin >> n;
	while (n--){
		for (int i = 0; i < 4; i++)
			cin >> x[i] >> y[i];
		if (abs((x[1] - x[0]) * (y[3] - y[2]) - (x[3] - x[2]) * (y[1] - y[0])) < EPS)
			cout << "YES" << endl;
		else
			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;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double AB = (y2-y1) / (x2-x1);
		double CD = (y4-y3) / (x4-x3);

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

	}
	return 0;
}

C++: #include <iostream>

int main(){
	int a;
	long double 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)){
			std::cout<<"YES"<<std::endl;
		}else{
			std::cout<<"NO"<<std::endl;
		}
		
    }
    return 0;
}

C++: #define _USE_MATH_DEFINES
 
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <math.h>

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

	return 0;
}

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

int main(){
  double a,b,c,d,e,f,g,h,m[4];
  int s;
  cin>>s;
  for(int j=0;j<s;j++){
    cin>>a>>b>>c>>d>>e>>f>>g>>h;
    m[0]=c-a;
    m[1]=g-e;
    m[2]=d-b;
    m[3]=h-f;
    if(m[2]*m[0]==m[3]*m[1])cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
  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,y1,x2,y2,x3,y3,x4,y4; 
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    double res1 = (x1 - x2)*(y3 - y4);
    double res2 = (y1 - y2)*(x3 - x4);

    if ( res1 == res2 ) cout << "YES" << endl;
    else cout << "NO" << endl;
  }

  return 0;
}

C++: #include <algorithm>
#include <functional>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <bitset>
#include <climits>

#define all(c) (c).begin(), (c).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define pb(e) push_back(e)
#define mp(a, b) make_pair(a, b)
#define fr first
#define sc second

const int INF=100000000;
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
using namespace std;
typedef pair<int ,int > P;
typedef long long ll;

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

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

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

    double X1 = x2-x1, Y1 = y2-y1;
    double X2 = x4-x3, Y2 = y4-y3;

    if(abs(X1*Y2-X2*Y1) < 1e-20) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
}

C++: #include <iostream>
using namespace std;
void judge(double,double,double,double,double,double,double,double);

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;
		judge(x1, y1, x2, y2, x3, y3, x4, y4);
	}
	
	return 0;
}

void judge(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) {
	double abx = x2 - x1;
	double aby = y2 - y1;
	double cdx = x4 - x3;
	double cdy = y4 - y3;
	if (abx * cdy == aby * cdx) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}

	return;

}

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
const double pi = acos(-1);
const double EPS = 1e-6;

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

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 (abs(cross(lineab,linecd)) < EPS) {
      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,value1,value2;
	int n;
	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);
		value1 = (y2-y1)/(x2-x1);
		value2 = (y3-y4)/(x3-x4);

		if(fabs(value1-value2)<0.000001){
			printf("YES\n");
		}else{
			printf("NO\n");
		}

	}
    return 0;
}

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

using namespace std;

int main (void) {
  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 t1 = (y1-y2)/(x1-x2));
    double t2 = (y3-y4)/(x3-x4));
    //cout << t1 << " " << t2 << endl;
    if ( t1 == t2 ) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  
  return 0;
}

C++: #include <iostream>
#include <cstdio>
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;
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		double v1x = x2-x1;
		double v1y = y2-y1;
		double v2x = x4-x3;
		double v2y = y4-y3;
		double op = v1x*v2y-v1y*v2x;
		if(op<0.000001) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}