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++: #include <iostream>
#include <cmath>

struct Vector2D {
	double x;
	double y;

	double abs() const {
		return std::sqrt(x * x + y * y);
	}
	Vector2D& operator-=(const Vector2D& rhs) {
		x -= rhs.x;
		y -= rhs.y;
		return *this;
	}
};

Vector2D operator-(const Vector2D& lhs, const Vector2D& rhs)
{
	return Vector2D(lhs) -= rhs;
}

int main()
{
	int count = 0;
	std::cin >> count;
	for (int i = 0; i < count; ++i) {
		Vector2D pA, pB, pC, pD;
		std::cin >> pA.x >> pA.y >> pB.x >> pB.y >> pC.x >> pC.y >> pD.x >> pD.y;

		Vector2D rAB(pB - pA), rCD(pD - pC);
		const double eps = 1.0e-8;
		if (rAB.abs() >= eps && rCD.abs() >= eps && std::abs(rAB.x * rCD.y - rAB.y * rCD.x) < eps) {
			std::cout << "YES\n";
		} else {
			std::cout << "NO\n";
		}
	}

	return 0;
}

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

int main() {
  int n = 0;
  cin >> n;

  for(int i = 0; i < n && 0 <= n && n < 100; i++) {
    double d[8];
    for(int j = 0; j < 4*2; j++)
      cin >> d[j];
    double tanAB = (d[3]-d[1])/(d[0]-d[2]);
    double tanCD = (d[7]-d[5])/(d[4]-d[6]);
    if(tanAB == tanCD)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <cassert>
#include <algorithm>
#include <functional>
#include <vector>
#include <string>
#include <cstring>
#include <stack>
#include <queue>
#include <map>
#include <bitset>
#include <sstream>
#include <istream>
#include <cmath>
#include <cstdio>

using namespace std;

#define vci vector<int>
#define vcs vector<string>
#define pb push_back
#define sz size()
#define mapci map<char, int>
#define mapsi map<string, int>
#define all(x) x.begin(), x.end()

#define for_(i, a, b) for (int i=(int)a; i<(int)b; i++)
#define for_d(i, a, b) for (int i=(int)a-1; i>=b; i--)
#define for_r(i, a, b, c) for (int i=(int)a; i<(int)b; i += c)
#define for_dr(i, a, b, c) for (int i=(int)a-1; i>=b; i -= c)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)

#define vcitr vector<int>::iterator
#define vcsitr vector<string>::iterator
#define mapcitr map<char, int>::iterator
#define mapsitr map<string, int>::iterator

typedef long long ll;

const int iINF = 2147483647;
const ll lINF = 9223372036854775807;

template <class T> inline void dbg(T t) { cout << t << endl; }

struct Point2D { 
	double x, y;
	Point2D (double a=0, double b=0) { x=a; y=b; }
};

int main() {
	int n; cin >> n;
	
	for (int i=0; i<n; i++) {
		Point2D a, b, c, d;
		
		cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y >> d.x >> d.y;
		
		double p = (a.y-b.y)/(a.x-b.x), q = (c.y-d.y)/(c.x-d.x);
		
		if (abs(p-q) < 1e9) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	
	return 0;
}

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

using uint=unsigned;
using ll=long long;
using ull=unsigned long long;
#define int ll

#define rng(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,b) rng(i,0,b)
#define gnr(i,a,b) for(int i=int(b)-1;i>=a;i--)
#define per(i,b) gnr(i,0,b)
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define fs first
#define sc second
#define bg begin()
#define ed end()
#define all(x) x.bg,x.ed
#ifdef LOCAL
#define dmp(x) cerr<<__LINE__<<" "<<#x<<" "<<x<<endl
#else
#define dmp(x) void(0)
#endif
#define tmp template<class t>

tmp void chmax(t&a,t b){if(a<b)a=b;}
tmp void chmin(t&a,t b){if(a>b)a=b;}

tmp using vc=vector<t>;
tmp using vvc=vc<vc<t>>;

using pi=pair<int,int>;
using vi=vc<int>;

template<class t,class u>
ostream& operator<<(ostream& os,const pair<t,u>& p){
	return os<<"{"<<p.fs<<","<<p.sc<<"}";
}

tmp ostream& operator<<(ostream& os,const vc<t>& v){
	os<<"{";
	for(auto e:v)os<<e<<",";
	return os<<"}";
}

constexpr ll ten(int n){
	return n==0?1:ten(n-1)*10;
}

tmp void mkuni(vc<t>&v){
	sort(all(v));
	v.erase(unique(all(v)),v.ed);
}

ll read(){ll i;cin>>i;return i;}

using ld=long double;
using cm=complex<ld>;
#define x real()
#define y imag()
const ld eps=1e-12;
int sgn(ld a){return a<-eps?-1:(a>eps?1:0);}
auto cmcmp=[](const cm&a,const cm&b){
	if(sgn(a.x-b.x))return a.x<b.x;
	else return sgn(a.y-b.y)<0;
};

struct ln{
	cm a,b;
	cm dir(){return b-a;}
};
ld dot(cm a,cm b){return a.x*b.x+a.y*b.y;}
ld crs(cm a,cm b){return a.x*b.y-a.y*b.x;}
int ccw(cm a,cm b){return sgn(crs(a,b));}
int ccw(cm a,cm b,cm c){return ccw(b-a,c-a);}
int ccw(ln a,cm b){return ccw(a.a,a.b,b);}

//(-2)[a,-1](0)[b,1](2)
int bet(cm a,cm b,cm c){
	cm d=b-a;
	ld e=dot(d,c-a);
	if(sgn(e)<=0)return sgn(e)-1;
	return sgn(e-norm(d))+1;
}

ld tri2(cm a,cm b,cm c){
	return crs(b-a,c-a);
}

cm readcm(){
	ld a,b;
	cin>>a>>b;
	return cm(a,b);
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(20);
	
	int n=read();
	
	rep(_,n){
		cm a=readcm();
		cm b=readcm();
		cm c=readcm();
		cm d=readcm();
		if(ccw(b-a,d-c)==0)
			cout<<"YES"<<endl;
		else
			cout<<"NO"<<endl;
	}
}

C++: #include <iostream>

int main() {
  int a, b;
  int i;

  double x[4];
  double y[4];

  bool isYes;

  std::cin >> a;

  for(i = 0; i < a; i++) {

    std::cin >> x[0] >> y[0];
    std::cin >> x[1] >> y[1];
    std::cin >> x[2] >> y[2];
    std::cin >> x[3] >> y[3];

    if( (x[1] - x[0]) != 0 ) {
      if( (x[3] - x[2]) != 0 ) {
	isYes = true;
      }
      else {
	isYes = false;
      }
    }
    else {
      if( (x[3] - x[2]) == 0 ) {
	isYes = true;
      }
      else {
	isYes = false;
      }
    }
      
    if( isYes ) {
      std::cout << "YES" << std::endl;
    }
    else {
      std::cout << "NO" << std::endl;
    }

  }
 
  return 0;
}