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>

using namespace std;

int main()
{
	double x1, y1, x2, y2, x3, y3, x4, y4;
	int N;
	cin >> N;
	
	for (int i=0; i<N; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		
		if ( ( (x1==x2) && (y1==y2) ) || ( (x3==x4) && (y3==y4) ) ) {
			cout << "NO" << endl;
			continue;
		}
		
		double LHS = 100000.0 * (y2 - y1) * (x4 - x3);
		double RHS = 100000.0 * (y4 - y3) * (x2 - x1);
		//cout << LHS << " " << RHS << endl;
		//if ( (y2 - y1) * (x4 - x3) == (y4 - y3) * (x2 - x1) ) cout << "YES" << endl;
		if ( LHS == RHS ) 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])==0){
cout<<"YES"<<endl;
}else{
cout<<"NO"<<endl;
}
}
return 0;
}

C++: #include <stdio.h>

int main() {
    double x1, y1, x2, y2, x3, y3, x4, y4;
    int i, n;
    
    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( ((x1-x2)*(y3-y4) == (y1-y2)*(x3-x4)) ) {
            printf("YES\n");
        } else {
            printf("NO\n");
        }
    }
    
    return 0;
}

C++: #include <iostream>
#include <cmath>
#include <complex>
using namespace std;
typedef complex<double> xy_t;
double cross_product(xy_t a, xy_t b){
  return (conj(a)*b).imag();
}

const double eps = 1e-11;
double x[4], y[4];
int N;
int main(){
  cin >> N;
  for(int t=0; t<N; t++){
    for(int i=0; i<4; i++){
      cin >> x[i] >> y[i];
    }
    xy_t a[2] = {
      xy_t(x[0],y[0]) - xy_t(x[1],y[1]),
      xy_t(x[2],y[2]) - xy_t(x[3],y[3])
    };
    bool p = abs(cross_product(a[0], a[1])) < eps;
    cout << (p ? "YES" : "NO") << endl;

  }
}

C++: #include <iostream>
#include <string>

class Point
{
public:
	double m_X;
	double m_Y;
	Point(double x, double y)
		: m_X( x )
		, m_Y( y )
	{}
};

class LineSegment
{
private:
	Point m_Start;
	Point m_End;
public:
	LineSegment(Point start, Point end)
		: m_Start( start )
		, m_End( end )
	{}
	double CalcSlope()
	{
		return((m_End.m_Y - m_Start.m_Y) / (m_End.m_X - m_Start.m_X));
	}
};

int main()
{
	int n = 0;
	double x1 = 0;
	double y1 = 0;
	double x2 = 0;
	double y2 = 0;
	double x3 = 0;
	double y3 = 0;
	double x4 = 0;
	double y4 = 0;

	std::cin >> n;

	for (int data_no = 0; data_no < n; ++data_no)
	{
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;

		Point start1{ x1, y1 };
		Point end1{ x2, y2 };
		Point start2{ x3, y3 };
		Point end2{ x4, y4 };

		LineSegment line1{ start1, end1 };
		double line1_slope = line1.CalcSlope();

		LineSegment line2{ start2, end2 };
		double line2_slope = line2.CalcSlope();

		if (line1_slope == line2_slope)
		{
			std::cout << "YES" << std::endl;
		}
		else
		{
			std::cout << "NO" << std::endl;
		}
	}

	return 0;
}

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

using namespace std;

int main() {
  int n;
  scanf("%d", &n);

  for (int c = 0; c < n; ++c) {
    double input[8];
    for (int i = 0; i < 8; ++i) {
      scanf("%lf", &input[i]);
    }
    pair<double, double> vec_a(input[2] - input[0], input[3] - input[1]);
    pair<double, double> vec_b(input[6] - input[4], input[7] - input[5]);
    double d_a = sqrt(pow(vec_a.first, 2.0) + pow(vec_a.second, 2.0));
    double d_b = sqrt(pow(vec_b.first, 2.0) + pow(vec_b.second, 2.0));
    double ip = vec_a.first * vec_b.first + vec_a.second * vec_b.second;
    
    if (abs(abs(ip) - d_a * d_b) < 0.0000001) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
}

C++: #include<iostream>
#include<cmath>
#include<cassert>
#include<cstdlib>
using namespace std;
#define EPS 0.0000001 
main(){
  int tcase;   cin >> tcase;
  double x1, y1, x2, y2, x3, y3, x4, y4;
  for ( int i = 0; i < tcase; i++ ){
      cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
      if ( abs((y2 - y1)*(x4 - x3) - (y4 - y3)*(x2 - x1) ) < EPS ) cout << "YES" << endl;
      else cout << "NO" << endl;
  }
}

C++: #include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y-1);(X) >=0;--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
  int i,j,k,T;
  cin>>T;
  while(T--){
    double x[4],y[4];
    rep(i,4)
      cin>>x[i]>>y[i];
    rep(i,2){
      x[i*2+1]-=x[i*2];
      y[i*2+1]-=y[i*2];
    }
    cout<<(x[1]*y[3]==x[3]*y[1]?"YES":"NO")<<endl;
  }
  return 0;
}