Go: package main

import (
        "fmt"
        "math/big"
)

func main() {
        var x1, x2, x3, x4, y1, y2, y3, y4 big.Float
        var n int
        fmt.Scanf("%d", &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)
                var lx, ly, mx, my, mul1, mul2, sub, zz big.Float
                lx.Sub(&x2, &x1)
                ly.Sub(&y2, &y1)
                mx.Sub(&x4, &x3)
                my.Sub(&y4, &y3)
                mul1.Mul(&lx, &my)
                mul2.Mul(&ly, &mx)
                sub.Sub(&mul1, &mul2)
                zz.SetFloat64(0.0)

                if sub.Cmp(&zz) == 0 {
                        fmt.Println("YES")
                } else {
                        fmt.Println("NO")
                }
        }
}

C++: /*
NOTE :
*min_element(.begin(),.end())
*max_element(.begin(),.end())
stack push pop top
queue push pop front
priority_queue<> pq
 push()  pop() size()  top()
map<>
 find() begin() end() insert(map<>::value_type())
pair<>
sort(.begin(), .end())
sort(arr, arr+N)
sort(a, a+N, greater<int>())
binary_search(vc.begin(), vc.end(), x)  //binary_search???true, false?????????
vector<int>::iterator lit = lower_bound(vc.begin(), vc.end(), x);
  lower_bound?????????????????????"??\???"????????????????????????????????????????????¬???????????????
vector<int>::iterator uit = upper_bound(vc.begin(), vc.end(), x);
  upper_bound????????????????????????"?¶???????"?????????????????????????????????????????¬???????????????
*/
#include <iostream>
#include <cstdio>
#include <climits>
#include <cmath>
#include <cassert>
#include <sstream>
#include <algorithm>
#include <valarray>
#include <utility>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <map>
#include <set>

#define MAX 100
#define INF 1<<20
#define LLINF 10e12 // 1<<31 // 2^31
#define REP(i,n) for(int i=0;i<n;i++)
#define REP2(i,a,n) for(int i=(a);i<(n);i++)
#define SET(a,c) memset(a,c,sizeof a)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define FOREACH(i,c) for(auto (i) : (c))
#define BIT(i,j) ((i)>>(j))&1
#define ALL(o) (o).begin(), (o).end()
#define ERASE(o) (o).erase(unique(ALL((o))), (o).end());

using namespace std;
typedef long long ll;
typedef valarray<int> array_t;
/////
double x[4], y[4];
bool solve()
{
  return (fabs((x[1]-x[0])*(y[3]-y[2])-(x[3]-x[2])*(y[1]-y[0]))==0);
}
int main()
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  // FROM HERE
  int n; cin >> n;
  REP(i,n)
  {
    REP(i,4) cin >> x[i] >> y[i];
    printf("%s\n",(solve()?"YES":"NO"));
  }
  return 0;
}

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

typedef complex<double> P;

// 許容する誤差ε
#define EPS (1e-10)
// 2つのスカラーが等しいかどうか
#define EQ(a,b) (abs((a)-(b)) < EPS)

// 外積 (cross product) : a×b = |a||b|sinΘ
double cross(P a, P b) {
  return (a.real() * b.imag() - a.imag() * b.real());
}

// 2直線の平行判定 : a//b <=> cross(a, b) = 0
int is_parallel(P a1, P a2, P b1, P b2) {
  return EQ( cross(a1-a2, b1-b2), 0.0 );
}

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

	cin >> n;
	for(int i=0 ; i<n ; i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		P a(x1,y1), b(x2,y2), c(x3,y3), d(x4,y4);
		if( is_parallel(a,b,c,d) ){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		}
	}
}

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;
double EPS = 1e-9;
// BEGIN //////////////////////////////////////////////////////////////


int main() {
	int N;
	cin >> N;
	double x1, y1, x2, y2, x3, y3, x4, y4;
	REP(i, N) {
		 scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);

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

	return 0;
}

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

C++: #include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
using namespace std;
typedef pair<int, int> P;

const double EPS = 1e-10;

signed main(){
    int n;
    cin >> n;
    double x[4], y[4];
    rep(i, 0, n){
        rep(j, 0, 4){
            cin >> x[j] >> y[j];
        }
        double h1, h2;
        int cnt = 0;
        if(fabs(x[1] - x[0]) < EPS) cnt++;
        else h1 = (y[1] - y[0]) / (x[1] - x[0]);
        if(fabs(x[3] - x[2]) < EPS) cnt++;
        else h2 = (y[3] - y[2]) / (x[3] - x[2]);
        if(fabs(h1 - h2) < EPS || cnt == 2) cout << "YES" << endl;
        else cout << "NO" << endl;
    }
}

C++: // うまくいくかどうかテスト
#include <iostream>
using namespace std;
int main(void) {
  int n;
  float x1, y1, x2, y2, x3, y3, x4, y4;
  cin >> n;
  while (n--) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if ((y1 - y2) / (x1 - x2) == (y3 - y4) / (x3 - x4)) {
      cout << "YES";
    } else {
      cout << "NO";
    }
    cout << endl;
  }
  return 0;
}

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

int main()
{
  double x1,x2,x3,x4,y1,y2,y3,y4;
  double dx1,dy1,dx2,dy2;
  int n;
  int i;

  cin>>n;
  for(i=0;i<n;i++){
    cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
    dx1=x2-x1;
    dy1=y2-y1;
    dx2=x4-x3;
    dy2=y4-y3;

    if(dx1==0 && dx2==0)
      cout<<"YES"<<endl;
    else if(dx1==0 || dx2==0)
      cout<<"NO"<<endl;
    else if(dy1/dx1 == dy2/dx2)
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
}

C++: // 0021.cpp : コンソール アプリケーションのエントリ ポイントを定義します。
//

#include "stdafx.h"
#include <iostream>
using namespace std;

#define EPS 1e-7

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;
		if (x1 == x2 && x3 == x4){
			cout << "YES" << endl;
		}
		else if (x1 == x2 || x3 == x4){
			cout << "NO" << endl;
		}
		else if (abs((y2 - y1) / (x2 - x1) - (y4 - y3) / (x4 - x3)) < EPS){
			cout << "YES" << endl;
		}
		else{
			cout << "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;
		if (x1 == x2 && x3 == x4){
			cout << "YES" << endl;
		}
		else if (x1 == x2 || x3 == x4){
			cout << "NO" << endl;
		}
		else if ((y2 - y1) * (x4 - x3) == (y4 - y3) * (x2 - x1)){
			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,y1,x2,y2,x3,y3,x4,y4;
		scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		if(y1==y2){
			if(y3==y4){
				printf("YES\n");
			}
			else printf("NO\n");
		}
		else if(y3==y4){
			printf("NO\n");
		}
		else{
			if((x1-x2)/(y1-y2)==(x3-x4)/(y3-y4)){
				printf("YES\n");
			}
			else printf("NO\n");
		}
	}
	return 0;
}