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 <cstdio>
#include <cstdlib>
#include <cstdint>
#include <cstring>
#include <cctype>
#include <iostream>
#include <sstream>
#include <vector>
#include <list>
#include <deque>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <algorithm>
#include <functional>
#include <complex>
using namespace std;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long long ll;
const double PI = 3.141592653589793238462643383279502884L;
const int LARGE_PRIME = 1000000007;
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define tr(c, i) for(auto i = (c).begin(); i != (c).end(); i++)
#define rtr(c, i) for(auto i = (c).rbegin(); i != (c).rend(); i++)
#define repfn(i,a,cont,next) \
  for(auto i = (a); [=](){return(cont);}(); i = [=](){return(next);}())
#define repby(i,a,b,s) repfn(i,a,i<b,i+s)
#define repab(i,a,b) repby(i,a,b,1)
#define rep(i,b) repab(i,0,b)
#define pb push_back
#define sz(c) int((c).size())

typedef complex<double> P;
const double precision = 1e-10;

bool EQ(double d, double e)
{
  return abs(d - e) < precision;
}

double cross(P a, P b)
{
  return a.real() * b.imag() - a.imag() * b.real();
}

bool parallel(P a, P b)
{
  return EQ(cross(a, b), 0.0);
}

int main(int argc, char **argv)
{
  vector<P> v(4);
  double x, y;
  int n;
  cin >> n;
  while (n--) {
    rep (i, 4) {
      cin >> x >> y;
      v[i] = P(x, y);
    }
    P p = v[1] - v[0];
    P q = v[3] - v[2];
    if (parallel(v[1] - v[0], v[3] - v[2]))
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }

  return 0;
}

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

int main(){
	int n;
	double x[4],y[4];
	cin>>n;
	for(;n--;){
		for(int i=0;i<4;i++){
			cin>>x[i];
			cin>>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;
}

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

int main(void) {
  int n;
  cin >> n;
  while (n--) {
    double x1, y1, x2, y2;
    double ang1, ang2;
    cin >> x1 >> y1 >> x2 >> y2;
    ang1 = (y2 - y1) / (x2 - x1);
    cin >> x1 >> y1 >> x2 >> y2;
    ang2 = (y2 - y1) / (x2 - x1);

    if (ang1 == ang2) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }

  return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <string.h>
#include <cmath>
using namespace std;

#define ISEQ(c) (c).begin(), (c).end()
typedef long long ll;

int main() {
  int n;
  scanf("%d", &n);
  double x[4], y[4];
  const double EPS = 1e-12;
  for (int z = 0; z < n; z++) {
    for (int i = 0; i < 4; i++) {
      scanf("%lf%lf", &x[i], &y[i]);
    }
    printf("%s\n", abs((y[1]-y[0])*(x[3]-x[2])-(y[3]-y[2])*(x[1]-x[0])) < EPS ? "YES" : "NO");
  }
}

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

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

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>

using namespace std;

#define FOR(i,a,b) for(long long i=(a);i<(b);i++)
#define REP(i,N) for(long long i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define fi first
#define se second

#define PI acos(-1.0)
#define INF 1000000007

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<double, double> PD;
typedef pair<string, ll> PS;
typedef vector<ll> V;

int n;
double x[100], y[100];

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

C++: #include <iostream>

using namespace std;
int main(void){
    // Here your code !
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;
if(x1==x2&&x3==x4) cout<<"YES"<<endl;
else if(y1==y2&&y3==y4) cout<<"YES"<<endl;
else{
    double a,b;
    a=(y2-y1)/(x2-x1);
    b=(y4-y3)/(x4-x3); 
    if( a ==b )
    cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
}
}
return 0;
}

C++: #include <stdio.h>
struct point{
    double x;
    double y;
};
double abs(double a){
    if(a>0)return a;
    return -a;
}
int main(){
    int n;
    point a[4];
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        for(int j=0;j<4;j++){
            scanf("%lf%lf",&a[j].x,&a[j].y);
        }
        if(a[1].x==a[0].x){
            if(a[3].x==a[2].x)printf("YES\n");
            else printf("NO\n");
        }
        else  if(a[1].y==a[0].y){
            if(a[3].y==a[2].y)printf("YES\n");
            else printf("NO\n");
        }
        else  if(a[3].x==a[2].x){
            printf("NO\n");
        }
        else if(a[3].y==a[2].y){
            printf("NO\n");
        }
        else if(abs(((a[1].x-a[0].x)*(a[3].y-a[2].y))-((a[3].x-a[2].x)*(a[1].y-a[0].y)))<=1e-9)printf("YES\n");
        else printf("NO\n");
    }
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <numeric>
#include <string>
#include <vector>
#include <list>
#include <iterator>

#include <cmath>

typedef std::pair<double,double> Vec;
typedef std::pair<Vec,Vec> Line;

Vec operator+(const Vec& lhs, const Vec& rhs) {
	return std::make_pair(lhs.first+rhs.first, lhs.second+rhs.second);
}

Vec operator-(const Vec& lhs, const Vec& rhs) {
	return std::make_pair(lhs.first-rhs.first, lhs.second-rhs.second);
}

Vec lineToVec(const Line& l) {
	return l.first - l.second;
}

double cross(const Vec& lhs, const Vec& rhs) {
  return lhs.first*rhs.second - lhs.second*rhs.first;
}

int main(void){
	using namespace std;

	int n;
	cin >> n;

	vector< pair<Line,Line> > input;
	input.reserve(n);

	for(int i=1; i<=n; i++){
		double x1,y1,x2,y2,x3,y3,x4,y4;
		cin
			>> x1 >> y1
			>> x2 >> y2
			>> x3 >> y3
			>> x4 >> y4;

		auto AB = make_pair( make_pair(x1,y1), make_pair(x2,y2) );
		auto CD = make_pair( make_pair(x3,y3), make_pair(x4,y4) );

		input.push_back(make_pair(AB,CD));
	}

	for(auto itr=input.begin(); itr!=input.end(); itr++){
		auto AB = itr->first;
		auto CD = itr->second;

		auto cr = cross( lineToVec(AB), lineToVec(CD) );

		if( abs(cr) <1e-10 ){
			cout << "YES";
		}
		else{
			cout << "NO";
		}
		if( distance( itr, input.end() )>1 ){
			cout << endl;
		}
	}
}