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 <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <string>
#include <cmath>
#include <complex>
#include <map>
using namespace std;

#define rep(i,n) for(int i=0;i<int(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define EPS 1e-11
#define F first
#define S second

static const double PI=6*asin(0.5);
typedef long long ll;
typedef complex<double> CP;
typedef pair<double,double> P;
static const int INF=1<<24;

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

C++: #include<iostream>

int main() {
	int n;
	std::cin >> n;
	for (int i = 0; i < n; i++) {
		double x1, y1, x2, y2, x3, y3, x4, y4, ax, ay, bx, by;
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		ax = x1 - x2; ay = y1 - y2;
		bx = x3 - x4; by = y3 - y4;

		if ((ax*ax + ay*ay) * (bx*bx + by*by) == (ax*bx + ay*by)*(ax*bx + ay*by)) {
			std::cout << "YES" << std::endl;
		}
		else {
			std::cout << "NO" << std::endl;
		}
	}

	return 0;
}

C++: #include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()
#define EPS 1e-9

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

double cross (double xa, double ya, double xb, double yb )
{
	return (xa*yb - xb*ya );
}

int main()
{
//	cut here before submit 
//	freopen ("testcase.Parallelism", "r", stdin );
	int n;
	scanf ("%d", &n );
	rep (i, n ){
		double x1, y1, x2, y2, x3, y3, x4, y4;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		double d = cross (x2-x1, y2-y1, x4-x3, y4-y3 );
		if (fabs (d ) < EPS ){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		} // end if
	} // end loop
		
	return 0;
}

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

using namespace std;

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

  double cx[4], cy[4];
  for (int i = 0 ; i < n; ++i) {
    for (int j = 0; j < 4; j++)
      cin >> cx[j] >> cy[j];
  
    double kx = (cy[1] - cy[0]) / (cx[1] - cx[0]);
    double ky = (cy[3] - cy[2]) / (cx[3] - cx[2]);
    
    if (kx == ky) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
}

C++: #include <cstdio>

using namespace std;

double x1,y1,x2,y2,x3,y3,x4,y4;
    

int main()
{
    int n; scanf( "%d\n", &n );
    while( n > 0 )
    {
        scanf("%lf %lf %lf %lf %lf %lf %lf %lf %lf\n", &x1, &y1, &y2, &y2, &y3, &y3, &y4, &y4 );
        double dx1 = x2 - x1, dx2 = x4 - x3, dy1 = y2 - y1, dy2 = y4 - y3;
        if( (dx1 == 0 && dx2 == 0) || (dy1 == 0 && dy2 == 0 ) )
        {
            printf( "YES\n" );
        }
        else
        {
            dy1 /= dx1;
            dy2 /= dx2;
            if( dy1 == dy2 || dy1 == -dy2 )
            {
                printf( "YES\n" );
            }
        }
        printf( "NO\n" );
        n--;
    }
    return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <sstream>
#include <utility>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define each(e,c) for(auto&e:c)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif

int main(){
    int n; cin>>n;
    rep(_,n){
        double x_,y_;
        ll x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                cin >> x_ >> y_;
                x[i][j] = x_*100000;
                y[i][j] = y_*100000;
            }
        }
        ll dx1=x[0][0]-x[0][1], dy1=x[1][0]-x[1][1];
        ll dx2=x[0][0]-x[0][1], dy2=x[1][0]-x[1][1];
        puts(dx1*dy2==dx2*dy1 ? "NO" : "YES");
    }
}