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++: #include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <functional>
#include <string>
#include <algorithm>
#include <climits>
#include <utility>

#define PRINT(STR) cout << STR << endl;
#define REP(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)
#define REG(i, a, b) for (int (i) = ((int)(a)); (i) < ((int)(b)); i++)
#define ALL(V) (V).begin(), (V).end()

typedef long long ll;

using namespace std;

int nextInt() { int n = -1; cin >> n; return n; }
double nextDouble() { double d = -1; cin >> d; return d; }
ll nextll() { ll n = -1; cin >> n; return n; }
string nextString() { string str; cin >> str; return str; }

int INF = 9999999;

// BEGIN //////////////////////////////////////////////////////////////


int main() {
	int N = nextInt();
	REP(i, N) {
		double x1 = nextDouble();
		double y1 = nextDouble();
		double x2 = nextDouble();
		double y2 = nextDouble();
		double x3 = nextDouble();
		double y3 = nextDouble();
		double x4 = nextDouble();
		double y4 = nextDouble();

		if (x2 - x1 == 0 && x4 - x3 == 0) {
			if (y2 - y1 == 0 || y4 - y3 == 0) {
				PRINT("NO");
			} else {
				PRINT("YES");
			}
		} else if (x2 - x1 == 0 || x4 - x3 == 0) {
			PRINT("NO");
		} else {
			if ((y2 - y1) / (x2 - x1) - (y4 - y3) / (x4 - x3) < 0.000006) {
				PRINT("YES");
			} else {
				PRINT("NO");
			}
		}
	}

	return 0;
}

// END   //////////////////////////////////////////////////////////////

C++: #include <stdio.h>

int main(){
    int n,i,j;
    double x[5],y[5];
    long long X[5],Y[5];
    scanf("%d",&n);
    for(i=0;i<n;i++){
        for(j=1;j<=4;j++){
            scanf("%lf %lf",&x[i],&y[i]);
            X[i] = (int)(x[i]*1000000);
            Y[i] = (int)(y[i]*1000000);
        }
        if((X[2]-X[1])*(Y[4]-Y[3])-(X[4]-X[3])*(Y[2]-Y[1])){
            printf("NO\n");
        }else{
            printf("YES\n");
        }
    }
}

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

struct Point2D {
    double x, y;

    Point2D() {}
    Point2D(double ax, double ay) {
        x = ax;
        y = ay;
    }
    Point2D operator -(Point2D &p) {
        return Point2D(x - p.x, y - p.y);
    }
    double slope(Point2D &p) {
        return (p.y - y) / (p.x - x);
    }
    double cross(Point2D &p) { // only z
        return x * p.y - y * p.x;
    }
};

namespace std {
    istream &operator>>(istream &is, Point2D &p) {
        is >> p.x >> p.y;
        return is;
    }

    ostream &operator<<(ostream &os, Point2D &p) {
        os << fixed << p.x << " " << p.y;
        return os;
    }
}

int main()
{
    int n;
    cin >> n;
    for (Point2D a, b, c, d; n-- && cin >> a >> b >> c >> d;)
        cout << ((a.slope(b) == c.slope(d)) ? "YES" : "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;
		//cout << (x1 - x2) * (y3 - y4) << endl;
		//cout << (y1 - y2) * (x3 - x4) << endl;
		if((x1 - x2) * (y3 - y4) == (y1 - y2) * (x3 - x4)) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

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

typedef complex<double> P;
const double eps = 1e-8;

bool cross(P a, P b) {
  return a.real()*b.imag() - a.imag()*b.real();
}

int main() {
  int Tc;
  cin >> Tc;
  while(Tc--) {
    vector<P> ps(4);
    for(int i = 0; i < 4; ++i) {
      cin >> ps[i].real() >> ps[i].imag();
    }
    if(abs(cross(ps[1]-ps[0], ps[3]-ps[2])) < eps) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
  return 0;
}

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_;
                y[i][j] = y_;
            }
        }
        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++: //Parallelism
#include<bits/stdc++.h>
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>
#include <vector>
#include <algorithm>

#define INPUT_FROM_FILE (0) 
#if INPUT_FROM_FILE
#include <fstream>
#endif

int main(int argc, char **argv){
	int n = 0;
	double x1, y1, x2, y2, x3, y3, x4, y4;

#if INPUT_FROM_FILE
	std::ifstream ifs("test.txt");
#endif

//#if INPUT_FROM_FILE
//	ifs >> n;
//#else
//	std::cin >> n;
//#endif
	scanf("%d", &n);

	for(int i = 0; i < n; i++){
#if INPUT_FROM_FILE
		ifs >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
#else
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		//std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
#endif

		//if(x2 - x1 == 0 && x4 - x3 == 0){
		//	std::cout << "YES" << std::endl;
		//}
		//else if(x2 - x1 == 0 || x4 - x3 == 0){
		//	std::cout << "NO" << std::endl;
		//}
		//else{
		//	double a0 = (y2 - y1) / (x2 - x1);
		//	double a1 = (y4 - y3) / (x4 - x3);

		//	if(a0 == a1){
		//		std::cout << "YES" << std::endl;
		//	}
		//	else{
		//		std::cout << "NO" << std::endl;
		//	}
		//}

		if(fabs((y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1)) < 0.0000000001){
			std::cout << "YES" << std::endl;
		}
		else{
			std::cout << "NO" << std::endl;
		}
	}

	return 0;
}

C++: #include<stdio.h>

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

	scanf("%d",&n);
	for(int x=0;x<n;x++)
	{
		for(;;)
		{
			scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
			if(x1>100||y1>100||x2>100||y2>100||x3>100||y3>100||x4>100||y4>100)
			{
			}
			else if(x1<-100||y1<-100||x2<-100||y2<-100||x3<-100||y3<-100||x4<-100||y4<-100)
			{
			}
			else
			{
				break;
			}
		}

		x2-=x1;
		y2-=y1;
		x1=0;
		y1=0;
		x4-=x3;
		y4-=y3;
		x3=0;
		y3=0;

		p=x2/y2;
		q=x4/y4;

		if(p==q)
		{
			printf("YES\n");
		}
		else
		{
			printf("NO\n");
		}
	}
	return 0;
}