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++: #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>
#include <algorithm>
using namespace std;

int main(){
	int n;cin >> n;
	float a[8];
	while(n--){
		for(int i = 0;i < 8;i++)cin >> a[i];
		double y1 = a[3]-a[1];double x1 = a[2]-a[0];
		double y2 = a[7]-a[5];double x2 = a[6]-a[4];
		double ans = y1/x1 - y2/x2;
		if(ans == 0)cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0; 
}

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

int cross(P a, P b, P c, P d);

int main(){
    int n;
    cin >>n;
    for(int i = 0; i < n; i++){
        P a, b, c, d;
        cin >>a.real() >>a.imag() >>b.real() >>b.imag() >>c.real() >>c.imag() >>d.real() >>d.imag();
        if(cross(a, b, c, d)){
            cout <<"Yes" <<endl;
        } else{
            cout <<"No" <<endl;
        }
        return 0;
    }
}
int cross(P a, P b, P c, P d){
    P x = a - b, y = c - d;
    int ret;
    if(!(x.real() * y.imag() - x.imag() * y.real())){
        ret = 1;
    } else{
        ret = 0;
    }
    return ret;
}

C++: #include <iostream>
#include <stdio.h>
#include <string.h>
#include <string>
#include <algorithm>

using namespace std;

void q21() {
	int N;
	cin >> N;
	for (int i = 0; i < N; i++) {
		double ax, ay, bx, by, cx, cy, dx, dy;
		cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy;
		if (bx - ax == 0 || dx - cx == 0) {
			if (bx - ax == dx - cx) {
				cout << "Yes" << endl;
				continue;
			}
		}
		else if ((by - ay) / (bx - ax) == (dy - cy) / (dx - cx)) {
			cout << "YES" << endl;
			continue;
		}
		cout << "NO" << endl;
	}
}

int main() {
	q21();
	return 0;
}

C++: #include <iostream>
#include <complex>
using namespace std;
 
int main()
{
    int n;
    cin>>n;
    complex<double> a,b,c,d;
    while(n--)
    {
        cin>>a.real()>>a.imag()>>b.real()>>b.imag()>>c.real()>>c.imag()>>d.real()>>d.imag();
        a=a-b;
        c=c-d;
 
        cout<<(a.real()*c.imag()-a.imag()*c.real()==0?"YES":"NO")<<endl;
    }
    return 0;
}

C++: #include <iostream>

using namespace std;

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

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

C++: #include<iostream>
using namespace std;
int main()
{
	int n;cin>>n;
	for(;n--;)
	{
		double a,b,c,d,e,f,g,h;cin>>a>>b>>c>>d>>e>>f>>g>>h;
		if(a==c&&e==g)cout<<(a==c&&e==g?"YES":"NO")<<endl;
		else cout<<((d-b)/(c-a)==(h-f)/(g-e)?"YES":"NO")<<endl;
	}
}

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

using namespace std;

typedef complex<double> xy_t;
double cross(xy_t a,xy_t b);

xy_t P[4];

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

  double x[4],y[4];
  
  for(int i=0;i<n;i++){
    cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];
    for(int j=0;j<4;j++){
      P[j]=xy_t(x[j],y[j]);
    }
    if(abs(cross(P[1]-P[0],P[3]-P[2]))<pow(10,-10)){
      cout << "YES" <<endl;
    }else{
      cout << "NO" <<endl;
    }
    
  }

  

}

double cross(xy_t a,xy_t b){return (conj(a)*b).imag();}

C++: #include <algorithm>
#include <cmath>
#include <iostream>
#include <map>
#include <queue>
#include <stack>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef pair<int, int> pint;
typedef pair<ll, ll> pll;
#define range(i, a, b) for (int i = a; i < b; ++i)
#define rep(i, n) range(i, 0, n)
const ll INF = 1e10;
#define pb push_back
const double eps = 1e-10;

int main()
{
    int n;
    cin >> n;
    rep(i, n)
    {
        vector<double> x(4), y(4);
        rep(j, 4) cin >> x[j] >> y[j];
        double a = (x[3] - x[2]) * (y[1] - y[0]) - (x[1] - x[0]) * (y[3] - y[2]);
        if (abs(a) > eps) {
            cout << "NO" << endl;
        } else {
            cout << "YES" << endl;
        }
    }
}

C++: #include<iostream>
#include<cmath>
#include<cassert>
#include<cstdlib>
using namespace std;
#define EPS 0.0000001
 
 
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(){
    double x1, y1, x2, y2, x3, y3, x4, y4, ab, cd;
    int n, r;

    cin >> n;
    while(n--){
        cin >>x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

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

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

int main()
{
	double x1, x2, x3, x4, y1, y2, y3, y4;
	int n, i;
	scanf("%d", &n);
	for (i = 0; i < n; i++)
	{
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &x2, &x3, &x4, &y1, &y2, &y3, &y4);
		double a1 = ((x2 - x1) / (y2 - y1)), a2 = ((x4 - x3) / (y4 - y3));
		if (a1 == a2)
		{
			printf("YES\n");
			continue;
		}
		else
		{
			printf("NO\n");
			continue;
		}
	}
	return 0;
}