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 <stdio.h>
 
int main(void) {
    int kaisu,i,j;
    double x[4],y[4];

    scanf("%d",&kaisu);
    for(i=0;i<kaisu;i++)
	{
        for(j=0;j<4;j++)
			scanf("%lf %lf",&x[j],&y[j]);
        if(x[0]==x[1]) 
		{
            if(x[2]==x[3])
				printf("YES\n");
            else 
				printf("NO\n");
        } 
		else if(x[2]==x[3])
			printf("NO\n");
        else 
		{
            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++: #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_ *1000000;
                y[i][j] = y_ *1000000;
            }
        }
        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 <bits/stdc++.h>
#include <vector>
using namespace std;
double x_1, y_1, x_2, y_2, x_3, y_3, x_4, y_4, a, b, x;
double gradien(double x_1, double y_1, double x_2, double y_2){
	double m = 0;
	m = (y_1 - y_2)/(x_1 - x_2);
	
	return m;
}
int main(){
	cin >> x;
	for(int i = 1; i <= x; i++){
		cin >> x_1 >> y_1 >> x_2 >> y_2 >> x_3 >> y_3 >> x_4 >> y_4;
		a = gradien(x_1, y_1, x_2, y_2);
		b = gradien(x_3, y_3, x_4, y_4);
		if(a == b){
			cout << "YES\n";
		}
		else{
			cout << "NO\n";
		}
	}
	return 0;
}

C++: #include <stdio.h>

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

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#include<set>
#include<complex>
#include<map>
#define vi vector<int>
#define vvi vector<vector<int> >
#define ll long long int
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vb vector<bool>
#define vc vector<char>
#define vs vector<string>
#define ld long double
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define loop(i,s,n) for(int i=s;i<n;i++)
#define CC puts("-------ok--------");
#define all(in) in.begin(), in.end()
using namespace std;
typedef pair<int, int> pii;
#define MAX 99999999
typedef pair<double,double> pdd;
int main(){
    pdd no1,no2,no3,no4;
    int n;cin>>n;
    rep(i,n){
        cin>>no1.first>>no1.second>>no2.first>>no2.second>>no3.first>>no3.second>>no4.first>>no4.second;
        double d1=(no2.second-no1.second)/(no2.first-no1.first);
        double d2=(no4.second-no3.second)/(no4.first-no3.first);
        if(d1==d2&&d1!=0))cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
    }
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cstdio>
#include<cmath>
#define pb(in,tmp) in.push_back(tmp)
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,b) loop(i,0,b)
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
using namespace std;
int main(void)
{
  int n;
  int i;
  cin>>n;
  rep(i,n){
    double x1,x2,x3,x4;
	double y1,y2,y3,y4;
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
	if(abs((x2-x1)*(y4-y3)-(x4-x3)*(y2-y1))<1e-10)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
}

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

int main()
{
	float ax,ay,bx,by,cx,cy,dx,dy;
	double katamuki[2];
	short n;
	cin>>n;
	
	for(int i=1;i<=n;i++){
		cin>>ax>>ay>>bx>>by>>cx>>cy>>dx>>dy;
		katamuki[0]=(by-ay)/(bx-ax);
		katamuki[1]=(dy-cy)/(dx-cx);
		cout<<((katamuki[0]==katamuki[1])?"YES":"NO")<<endl;
	}
	
	return 0;
}

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

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

C++: #include <iostream>
#include <stdio.h>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <complex>
#include <map>
using namespace std;
typedef long long ll;
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<VI> VVI;
#define rep(i,n) for (int i=0; i < (n); i++)

typedef double D;      // 座標値の型。doubleかlong doubleを想定
typedef complex<D> P;  // Point
typedef pair<P, P> L;  // Line
typedef vector<P> VP;
const D EPS = 1e-9;    // 許容誤差。問題によって変える
#define X real()
#define Y imag()
#define LE(n,m) ((n) < (m) + EPS)
#define GE(n,m) ((n) + EPS > (m))
#define EQ(n,m) (abs((n)-(m)) < EPS)

// 内積　dot(a,b) = |a||b|cosθ
D dot(P a, P b) {
  return (conj(a)*b).X;
}
// 外積　cross(a,b) = |a||b|sinθ
D cross(P a, P b) {
  return (conj(a)*b).Y;
}

// 点の進行方向
int ccw(P a, P b, P c) {
  b -= a;  c -= a;
  if (cross(b,c) >  EPS) return +1;  // counter clockwise
  if (cross(b,c) < -EPS) return -1;  // clockwise
  if (dot(b,c)   < -EPS) return +2;  // c--a--b on line
  if (norm(b) < norm(c)) return -2;  // a--b--c on line or a==b
  return 0;                          // a--c--b on line or a==c or b==c
}

/* 交差判定　直線・線分は縮退してはならない。接する場合は交差するとみなす。isecはintersectの略 */

// 直線と点
bool isecLP(P a1, P a2, P b) {
  return abs(ccw(a1, a2, b)) != 1;  // return EQ(cross(a2-a1, b-a1), 0); と等価
}

// 直線と直線
bool isNotParallel(P a1, P a2, P b1, P b2) {
  return !isecLP(a2-a1, b2-b1, 0);
}

int main() {
  int n;
  cin >> n;
  rep(_,n) {
    VP ps(4);
    rep(i,4) {
      D x,y;
      cin >> x >> y;
      ps[i] = P(x,y);
    }
    cout << (isNotParallel(ps[0], ps[1], ps[2], ps[3]) ? "NO" : "YES") << endl;
  }
  return 0;
}

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

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