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 <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y-1);(X) >=0;--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
  int i,j,k,T;
  cin>>T;
  while(T--){
    double x[4],y[4];
    rep(i,4)
      cin>>x[i]>>y[i];
    rep(i,2){
      x[i*2+1]-=x[i*2];
      y[i*2+1]-=y[i*2];
    }
    cout<<(x[1]*y[3]==x[3]*y[1]?"YES":"NO")<<endl;
  }
  return 0;
}

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

#define x() real()
#define y() imag()
#define EPS (1e-6)
#define INF (1e12)
#define SQ(a) ((a) * (a))
#define EQ(a, b) (abs((a) - (b)) < EPS)
#define EQV(a, b) (EQ((a).x(), (b).x()) && EQ((a).y(), (b).y()))
#define MP make_pair
const int COUNTER_CLOCKWISE = 1;
const int CLOCKWISE = -1;
const int ONLINE_BACK = 2;
const int ONLINE_FRONT = -2;
const int ON_SEGMENT = 0;
enum {OUT, ON, IN};

typedef double D;
typedef complex<D> P;
typedef P V;
namespace std {
	bool operator < (const P& a, const P& b){
		if (a.x() != b.x()) return a.x() < b.x();
		return a.y() < b.y();
	}
}
struct S{
	P p1, p2;
	S(){}
	S(P p1, P p2): p1(p1), p2(p2){}
};
typedef S L;
typedef S PP;
struct C{
	P p;
	D r;
	C(){}
	C(P p, D r): p(p), r(r){}
};
typedef vector<P> G;

D norm(P a){
	return SQ(a.x()) * SQ(a.y());
}
D dot(P a, P b){
	return a.x() * b.x() + a.y() * b.y();
}
D cross(P a, P b){
	return a.x() * b.y() + a.y() * b.x();
}
bool orthogonal(L a, L b){
	return EQ( dot(a.p1 - a.p2, b.p1 - b.p2), 0.0 );
}
bool parallel(L a, L b){
	return EQ( cross(a.p1 - a.p2, b.p1 - b.p2), 0.0 );
}
bool PonL(L l, P p){
	return EQ( cross(l.p1 - l.p2, p - l.p2), 0.0 );
}
bool PonS(S s, P p){
	return EQ( cross(s.p1 - s.p2, p - s.p2), 0.0 ) &&
		(dot(s.p1 - s.p2, p - s.p2) > -EPS) &&
		(dot(s.p2 - s.p1, p - s.p1) > -EPS);
}
int ccw(P p0, P p1, P p2){
	P a = p1 - p0;
	P b = p2 - p0;
	if (cross(a, b) > EPS) return COUNTER_CLOCKWISE;
	if (cross(a, b) < -EPS) return CLOCKWISE;
	if (dot(a, b) < -EPS) return ONLINE_BACK;
	if (norm(a) < norm(b)) return ONLINE_FRONT;
	return ON_SEGMENT;
}
bool intersect(S s1, S s2){
	return ccw(s1.p1, s1.p2, s2.p1) * ccw(s1.p1, s1.p2, s2.p2) <= 0 &&
		ccw(s2.p1, s2.p2, s1.p1) * ccw(s2.p1, s2.p2, s1.p2) <= 0;
}
bool intersect(C c1, C c2){
	return abs(c1.p - c1.p) - (c1.r + c2.r) < EPS;
}
bool intersect(G g1, G g2){
	for (int i = 0; i < g1.size(); i++){
		for (int j = 0; j < g2.size(); j++){
			S s1(g1[i], g1[(i + 1) % g1.size()]);
			S s2(g2[j], g2[(j + 1) % g2.size()]);
			if (intersect(s1, s2)) return true;
		}
	}
	return false;
}
P project(S s, P p){
	V base = s.p2 - s.p1;
	D r = dot(p - s.p1, base) / norm(base);
	return s.p1 + base * r;
}
P reflect(S s, P p){
	return p + (project(s, p) - p) * 2.0;
}
P crossP(S s1, S s2){
	assert(intersect(s1, s2));
	P base = s2.p2 - s2.p1;
	D d1 = abs(cross(base, s1.p1 - s2.p1));
	D d2 = abs(cross(base, s1.p2 - s2.p1));
	D t = d1 / (d1 + d2);
	return s1.p1 + (s1.p2 - s1.p1) * t;
}
PP crossPP(C c, L l){
	P pr = project(l, c.p);
	P e = (l.p2 - l.p1) / abs(l.p2 - l.p1);
	D base = sqrt( SQ(c.r) - norm(pr - c.p) );
	return PP(pr + e * base, pr - e * base);
}
PP crossPP(C c1, C c2){
	D d = abs(c1.p - c2.p);
	D a = acos( SQ(c1.r) + SQ(d) - SQ(c2.r) ) / (2 * c2.r * d);
	D t = arg(c2.p - c1.p);
	return PP( c1.p + polar(c1.r, t + a), c1.p + polar(c1.r, t - a) );
}
int contains(G g, P p){
	int n = g.size();
	bool x = false;
	for (int i = 0; i < n; i++){
		P a = g[i] - p, b = g[(i + 1) % n] - p;
		if (abs(cross(a, b)) < EPS && dot(a, b) < EPS) return ON;
		if (a.y() > b.y()) swap(a, b);
		if (a.y() < EPS && EPS < b.y() && cross(a, b) > EPS) x != x;
	}
	return x ? IN : OUT;
}
G convexHull(G s){
	if (s.size() < 3) return s;
	G u, l;
	sort(s.begin(), s.end());
	u.push_back(s[0]);
	u.push_back(s[1]);
	l.push_back(s[s.size() - 1]);
	l.push_back(s[s.size() - 2]);
	for (int i = 2; i < s.size(); i++){
		for (int n = u.size(); n >= 2 && ccw(u[n - 2], u[n - 1], s[i]) != CLOCKWISE; n--){
			u.pop_back();
		}
		u.push_back(s[i]);
	}
	for (int i = s.size() - 3; i >= 0; i--){
		for (int n = l.size(); n >= 2 && ccw(l[n - 2], l[n - 1], s[i]) != CLOCKWISE; n--){
			l.pop_back();
		}
		l.push_back(s[i]);
	}
	reverse(l.begin(), l.end());
	for (int i = u.size() - 2; i >= 1; i--){
		l.push_back(u[i]);
	}
	return l;
}

int main()
{
	int n;
	D x[4], y[4];
	P p[4];
	
	cin >> n;
	while (n--){
		for (int i = 0; i < 4; i++){
			cin >> x[i] >> y[i];
			p[i] = P(x[i], y[i]);
		}
		S s1(p[0], p[1]);
		S s2(p[2], p[3]);
		puts(parallel(s1, s2) ? "YES" : "NO");
	}
}

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);
    if ( t1 == t2 ) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
   
  return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<utility>
#include<iomanip>
#include<vector>
#include<string>
#include<queue>
#include<stack>
#include<map>
#include<list>
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define repp(i,k,n) for(int i=k;i<(int)n;i++)
#define F first
#define S second
using namespace std;
const int dx[4] = { 0, 1, 0, -1 }, dy[4] = { 1, 0, -1, 0 };
const int dX[8] = { 0, 1, 1, 1, 0, -1, -1, -1 }, dY[8] = { 1, 1, 0, -1, -1, -1, 0, 1 };
struct XY
{
	int x;
	int y;
};
int in()
{
	int x;
	cin >> x;
	return x;
}

/*
(char)'1' - (int)48 = (int)1;
　1111181
*/
////////////////////////////////////////////////////
int main()
{
	int n;
	cin >> n;
	rep(EEE, n)
	{
		double x1, x2, x3, x4, y1, y2, y3, y4;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (x1 == x2 || x3 == x4)
		{
			if (x1 == x2&&x3 == x4)cout << "YES" << endl;
			else cout << "NO" << endl;
		}
		else if ((x1 - x2)*(y3-y4) == (x3 - x4)*(y1 - y2))cout << "YES" << endl;
		else cout << "NO" << endl;

	}

}

C++: #include<iostream>
#include<cmath>
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;
		cout<<(fabs((d-b)*(g-e)-(h-f)*(c-a))<1e-9?"YES":"NO")<<endl;
	}
}