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<iostream>
#include<queue>
#include<string>
#include<stack>
#include<cstdio>
#include<algorithm>

using namespace std;

int main(void)
{
  double x,y;
  double x1,y1;
  int n;
  int i;
  long double a=0,b=0;
  int k=0;
  int j=0;

  cin>>n;

  for(i=0;i<n;i++)
    {
      cin>>x>>y>>x1>>y1;
      if(x1-x!=0.0)
	{
          a=(y1-y)/(x1-x);
          j++;
	}
      else
        k++;

      cin>>x>>y>>x1>>y1;
      if(x1-x!=0.0)
	{
          b=(y1-y)/(x1-x);
          j++;
	}
      else
        k++;

      if((a==b && j==2) || k==2)
        puts("YES");
      else
        puts("NO");
    }

}

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 dx1 = x2-x1,
			   dy1 = y2-y1,
			   dx2 = x4-x3,
			   dy2 = y4-y3;
		
		if (dx2 * dy1 == dx1 * dy2) {
			if (dx1*dy1*dx2*dy2 != 0.0) {
				cout << "YES" << endl;
			} else {
				if (dx2+dy2 == 0.0 || dx1+dy1 == 0.0) {
					cout << "NO" << endl;
				} else {
					cout << "YES" << endl;
				}
			}
		} else {
			cout << "NO" << endl;
		}
	}
	return 0;
}

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

int main()
{
	int n ;
	double ax,ay,bx,by,cx,cy,dx,dy,a,b ;

	cin >> n ;
	for( int i = 0 ; i < n ; i ++ )
	{
		cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy ;

		a = (ay-by)/(ax-bx) ;
		b = (cy-dy)/(cx-dx) ;

		if( a == b )
		{
			cout << "YES" << endl ;
		}
		else
		{
			cout << "NO" << endl ;
		}
	}
	return 0 ;
}

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

}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <sstream>
#include <utility>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define each(e,c) for(auto&e:c)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif

int main(){
    int n; cin>>n;
    rep(_,n){
        ll x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = x_ *100000 + 0.5;
                y[i][j] = y_ *100000 + 0.5;
            }
        }
        ll dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        ll dx2=x[1][0]-x[1][1], dy2=y[1][0]-y[1][1];
        dump(dx1,dx2,dy1,dy2);
        puts(dx1*dy2==dx2*dy1 ? "YES" : "NO");
    }
}

C++: #include <iostream>

using namespace std;

int main(){
	int n;
	float x1,y1,x2,y2,x3,y3,x4,y4,s1,s2;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		s1=(y2-y1)/(x2-x1);
		s2=(y4-y3)/(x4-x3);
		if(s1==s2){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;	
		}
	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
#include <string>
#include <map>
#include <functional>
#include <cmath>
#include <cstdio>
using namespace std;

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

C++: #include<stdio.h>

int main(void){
	double x[4],y[4];
	int n,i;
	
	scanf("%d",&n);
	
	for(i=0;i<n;i++){
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2],&x[3],&y[3]);
		
		if(((y[1]-y[0])/(x[1]-x[0])) == ((y[3]-y[2])/(x[3]-x[2])))printf("YES\n");
		else printf("NO\n");
	}
	
	return 0;
}

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

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		double x[4], y[4];
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

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




	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <numeric>
#include <string>
#include <vector>
#include <list>
#include <iterator>

#include <cmath>

typedef std::pair<double,double> Vec;
typedef std::pair<Vec,Vec> Line;

Vec operator+(const Vec& lhs, const Vec& rhs) {
	return std::make_pair(lhs.first+rhs.first, lhs.second+rhs.second);
}

Vec operator-(const Vec& lhs, const Vec& rhs) {
	return std::make_pair(lhs.first-rhs.first, lhs.second-rhs.second);
}

Vec lineToVec(const Line& l) {
	return l.first - l.second;
}

double cross(const Vec& lhs, const Vec& rhs) {
  return lhs.first*rhs.second - lhs.second*rhs.first;
}

int main(void){
	using namespace std;

	int n;
	cin >> n;

	vector< pair<Line,Line> > input;
	input.reserve(n);

	double x1,y1,x2,y2,x3,y3,x4,y4;
	while(cin
		>> x1 >> y1
		>> x2 >> y2
		>> x3 >> y3
		>> x4 >> y4){

		auto AB = make_pair( make_pair(x1,y1), make_pair(x2,y2) );
		auto CD = make_pair( make_pair(x3,y3), make_pair(x4,y4) );

		input.push_back(make_pair(AB,CD));
	}

	for(auto itr=input.begin(); itr!=input.end(); itr++){
		auto AB = itr->first;
		auto CD = itr->second;

		auto cr = cross( lineToVec(AB), lineToVec(CD) );

		if( abs(cr) <10e-10 ){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}
	}
}

C++: #include<iostream>

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

  std::cin >> n;

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

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

int main() {
  int n;
  double x[4];
  double y[4];
  const double eps = 1.0e-12;

  scanf("%d", &n);
  while (n--) {
    for (int i=0; i<4; i++) {
      scanf("%lf %lf", &x[i], &y[i]);
    }
    if (abs((y[1]-y[0])*(x[3]-x[2]) - (x[1]-x[0])*(y[3]-y[2])) < eps) {
      printf("YES\n");
    } else {
      printf("NO\n");
    }
  }

  return 0;
}