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>
#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <algorithm>
using namespace std;
#define INF 0x7FFFFFFF

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

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

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

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

C++: #include <iostream>
using namespace std;
int n;
double xa,xb,xc,xd,ya,yb,yc,yd,ta,tb,tc,td;
int main(){
	int i;
	cin >> n;
	for(i=0;i<n;i++){
		cin >> xa >> ya >> xb >> yb >> xc >> yc >> xd >> yd;
		ta = xa - xb;
		tb = ya - yb;
		tc = xc - xd;
		td = yc - yd;
		if(tc/td == ta/tb) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

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

typedef struct xyz{
    double x;
    double y;
}XYZ;

int main(void){

    int times;
    cin >> times;

    XYZ a,b,c,d;
    double x1,y1,x2,y2;

    while(times > 0){
        cin >> a.x >> a.y;
        cin >> b.x >> b.y;
        cin >> c.x >> c.y;
        cin >> d.x >> d.y;

        x1 = a.x - b.x;
        y1 = a.y - b.y;
        x2 = c.x - d.x;
        y2 = c.y - d.y;

        if((y1 / x1) ==(y2 == x2)){
            cout << "YES" << endl;
        }else{
            cout << "NO" << endl;
        }

        times--;
    }


    return 0;
}

C++: #include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <ctime>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <set>
#include <map>
#include <iostream>
#include <deque>
#include <complex>
#include <string>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <valarray>
#include <iterator>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) container.begin(), container.end()
#define RALL(container) container.rbegin(), container.rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;

#define X real()
#define Y imag()

typedef complex<double> P;
struct L{
	P p1, p2;
	L(P p1, P p2):p1(p1), p2(p2){}
	L(){}
};
istream& operator>>(istream &is, P &p) {
	double x, y;
	is >> x >> y;
	p = P(x, y);
	return is;
}
inline int sig(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
inline double norm(const P &p){return p.X*p.X+p.Y*p.Y;}
inline double inp(const P& a, const P& b){return (conj(a)*b).X;}
inline double outp(const P& a, const P& b){return (conj(a)*b).Y;}


int T;

int main(){
	ios::sync_with_stdio(false);
	cin >> T;
	while(T--){
		P p1, p2, p3, p4;
		cin >> p1 >> p2 >> p3 >> p4;
		puts(!sig(outp(p2-p1, (p4-p3))) ? "YES" : "NO");
	}
	return 0;
}

C++: #include <stdio.h>
#include <cctype>
#include <limits.h>
#include <math.h>
#include <complex>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <algorithm>
#include <iomanip>
#include <iostream>

#define VARIABLE(x) cerr << #x << "=" << x << endl
#define BINARY(x) static_cast<bitset<16> >(x)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define REP(i,m,n) for (int i=m;i<(int)(n);i++)
#define if_range(x, y, w, h) if (0<=(int)(x) && (int)(x)<(int)(w) && 0<=(int)(y) && (int)(y)<(int)(h))
#define ALL(a) (a).begin(),(a).end()
const int INF = 1e9;
const double PI = 3.14159;
int dx[4]={0, 1, 0, -1}, dy[4]={-1, 0, 1, 0};
using namespace std;
typedef long long ll;
//typedef pair<int, int> P;

/* struct P {
	int x, y, n;
	P(int n, int x, int y):n(n), x(x), y(y){}
	P(){}
}; */


/** 幾何ライブラリ **/
// to do : 1183

#include <complex>

#define X real()
#define Y imag()

const double EPS = 1e-8;

typedef double D;
typedef complex<D> P; // Point

// 共役複素数 conj(a);

// 符号
int sig(D a, D b=0) { return a < b - EPS ? -1 : (a > b + EPS ? 1 : 0); }

// 内積
D dot_product(P a, P b) { return (conj(a)*b).real(); }

// 外積
D cross_product(P a, P b) { return (conj(a)*b).imag(); }

/** Problem0021 : Parallelism **/
int main()
{
	int N; cin>>N;
	rep(i, N) {
		P a, b;
		D x1, y1, x2, y2;
		cin>>x1>>y1>>x2>>y2;
		a.X = (x2 - x1);
		a.Y = (y2 - y1);
		
		cin>>x1>>y1>>x2>>y2;
		b.X = (x2 - x1);
		b.Y = (y2 - y1);
		
		if (abs(cross_product(a, b))<EPS) {
			cout << "YES" << endl;
		} else {
			cout << "NO" << endl;
		}
	}
}

C++: #include <functional>
#include <algorithm>
#include <iostream>
#include <numeric>
#include <iomanip>
#include <utility>
#include <cstdlib>
#include <sstream>
#include <bitset>
#include <vector>
#include <cstdio>
#include <ctime>
#include <queue>
#include <deque>
#include <cmath>
#include <stack>
#include <list>
#include <map>
#include <set>

using namespace std;


#define rep(i,n) for(int i=0;i<(n);i++)

const double EPS = 1e-6;
const double INF = 100000000;




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

    return 0;
}