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 <bits/stdc++.h>

using namespace std;

#define EPS 1e-10
#define equals(a, b) (fabs(a - b) < EPS)

struct Point {
    double x, y;

    Point(){}
    Point(double x, double y) : x(x), y(y) {}
 
    Point operator - (const Point &p) const {  return Point(x - p.x, y - p.y); }
};

typedef Point Vector;

double cross(const Point &a, const Point &b)
{
    return a.x * b.y - b.x * a.y;
}

struct Line {
    Point s, t;
    Line(){}
    Line(Point s, Point t) : s(s), t(t) {}
};

bool isParallelSS(const Line &s1, const Line &s2)
{
    Vector a = s1.t - s1.s;
    Vector b = s2.t - s2.s;
    return equals(cross(a, b), 0);
}

istream &operator >> (istream &is, Point &p)
{
    return is >> p.x >> p.y;
}

int main()
{
    int N;
    Line l[2];
    cin >> N;
    while (N--) {
        for (int i = 0; i < 2; i++) {
            cin >> l[i].s >> l[i].t;
        }
        cout << (isParallelSS(l[0], l[1]) ? "YES" : "NO") << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main() {
	int n;
	cin >> n;
	for (int z = 0; z < n; z++) {
		long float x1, x2, x3,y1, y2, y3, y4, x4 ;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (y1 > y2) {
			swap(y1, y2);
			swap(x1, x2);
		}
		if (y3 > y4) {
			swap(y3, y4);
			swap(x3, x4);
		}
		if ((x1 > x2&&x3 > x4 && ((y2 - y1) / (x1 - x2) == (y4 - y3) / (x3 - x4))) || (x2 > x1&&x4 > x3 && ((y1 - y2) / (x2 - x1) == (y3 - y4) / (x4 - x3)))) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}

C++: #include<iostream>
 
using namespace std;
 
int main(void)
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        double x1,y1,x2,y2,x3,y3,x4,y4;
        cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
        double a1,a2;
        a1=(y2-y1)/(x2-x1);
        a2=(y4-y3)/(x4-x3);
        if(a1==a2)
        {
            cout<<"YES"<<endl;
        }
        else{
            cout<<"NO"<<endl;
        }
    }
}

C++: #include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit(b) (1ll << (b))

using namespace std;

using i32 = int;
using i64 = long long;
using u64 = unsigned long long;
using f80 = long double;
using vi32 = vector<i32>;
using vi64 = vector<i64>;
using vu64 = vector<u64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() { cout << "Yes" << '\n'; exit(0); }
inline void no() { cout << "No" << '\n'; exit(0); }
inline i64 gcd(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); if (a % b == 0) return b; return gcd(b, a % b); }
inline i64 lcm(i64 a, i64 b) { return a / gcd(a, b) * b; }
inline u64 xorshift() { static u64 x = 88172645463325252ull; x = x ^ (x << 7); return x = x ^ (x >> 9); }
void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(16); solve(); return 0; }
template <typename T> class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T> class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { if (x < y) x = y; }
template <typename T> inline void amin(T &x, T y) { if (x > y) x = y; }
template <typename T> inline T power(T x, i64 n, T e = 1) { T r = e; while (n > 0) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; }
template <typename T> istream& operator>>(istream &is, vector<T> &v) { each(x, v) is >> x; return is; }
template <typename T> ostream& operator<<(ostream &os, vector<T> &v) { rep(i, v.size()) { if (i) os << ' '; os << v[i]; } return os; }
template <typename T, typename S> istream& operator>>(istream &is, pair<T, S> &p) { is >> p.first >> p.second; return is; }
template <typename T, typename S> ostream& operator<<(ostream &os, pair<T, S> &p) { os << p.first << ' ' << p.second; return os; }

void solve() {
  int n; cin >> n;
  while (n--) {
    vector<pair<f80, f80>> xy(4);
    rep(i, 4) cin >> xy[i];
    f80 k0 = (xy[1].second - xy[0].second) / (xy[1].first - xy[0].first);
    f80 k1 = (xy[3].second - xy[2].second) / (xy[3].first - xy[2].first);
    if (k0 == k1) {
      cout << "YES" << '\n';
    } else {
      cout << "NO" << '\n';
    }
  }
}

C++: #include "bits/stdc++.h"
using namespace std;
using ll = long long;
using vi = vector<int>;
using vii = vector<vector<int>>;
using vl = vector<ll>;
using vll = vector<vector<ll>>;
using pii = pair<int,int>;
#define FOR(i,a,b) for(ll i = (a); i < (b); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(obj) (obj).begin(), (obj).end()
#define pb push_back
const double pi = acos(-1);
const double EPS = 1e-10;

double cross(pair<double,double> c,pair<double,double> d){
  return c.first * d.second - d.first * c.first;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  vector<pair<double,double>> a(4);
  int n;
  pair<double,double> lineab, linecd;
  cin >> n;
  REP(i,n){
    REP(j,4){
      cin >> a[j].first >> a[j].second;
    }
    lineab.first = a[1].first - a[0].first;
    linecd.first = a[3].first - a[2].first;
    lineab.second = a[1].second - a[0].second;
    linecd.second = a[3].second - a[2].second;
    if (fabs(cross(lineab,linecd)) < EPS) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  
  
  return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main(){
	int n;
	cin >> n;
	while(n--){
		double x[4], y[4], p1 ,p2;
		for(int i = 0; i < 4; i++) cin >> x[i] >> y[i];
		p1 = (y[1] - y[0]) / (x[1] - x[0]);
		p2 = (y[3] - y[2]) / (x[3] - x[2]);
		if(abs(p1 - p2) < 1e-10) cout << "YES" << endl;
		else cout << "NO" << endl;	
	}
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
#define int long long
signed main(){
        int n;
        scanf("%lld",&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);
                double c1 = (y2-y1)/(x2-x1);
                double c2 = (y4-y3)/(x4-x3);
                if((x2-x1==0 && x4-x3==0) || fabs(c1-c2) <= 1E-10) printf("YES\n");
                else printf("NO\n");
        }
        return 0;
}