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;
long double x[4], y[4], xp[2], yp[2]; int n;
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];
		xp[0] = x[0] - x[1];
		yp[0] = y[0] - y[1];
		xp[1] = x[2] - x[3];
		yp[1] = y[2] - y[3];
		if (yp[0] == 0 && yp[1] == 0) { goto E; }
		if (yp[0] == 0 && yp[1] != 0) { goto F; }
		if (yp[0] != 0 && yp[1] == 0) { goto F; }
		if ((xp[0] / yp[0]) == (xp[1] / yp[1])) { goto E; }
		goto F;
	E:; cout << "YES" << endl;
		goto G;
	F:; cout << "NO" << endl;
	G:;
	}
}

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;
        if ((x2-x1)==0 || (x4-x3)==0)
            cout << (((x2-x1)==0&&(x4-x3)==0)? "YES" : "NO") << endl;
        else
            cout << (((y2-y1)/(x2-x1) == (y4-y3)/(x4-x3))? "YES" : "NO") << endl;
    }
    return 0;
}

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

using namespace std;

#define rep(i, n) for(int i = 0; i < (int)n; ++i)
#define repf(i, f, l) for(int i = f; i < (int)l; ++i)

#ifdef ONLINE_JUDGE
#define DEBUG false
#else
#define DEBUG true
#endif

#define pb emplace_back
#define lb lower_bound
#define ul unsigned long
#define ull unsigned long long
#define ll long long
#define INF 1000000007
#define MOD 1000000007
#define fs first
#define sd second

#define ALL(c) (c).begin(),(c).end()

#define DBG0(x)    {if(DEBUG){ cout << #x << ": " << x << "\t"; }}
#define DBG(x)     {if(DEBUG){DBG0(x); cout << endl;}}
#define DBG2(x, y) {if(DEBUG){DBG0(x); DBG(y);}}
#define DBG3(x, y, z) {if(DEBUG){DBG0(x); DBG2(y, z);}}
#define DBG4(w, x, y, z) {if(DEBUG){DBG0(w); DBG3(x, y, z);}}

const double EPS = 1.0e-11;
template <class T>
ostream& operator<<(ostream& os, vector<T> xs){ for(T x: xs) os << x << ' '; return os; }
template <class S, class T>
ostream& operator<<(ostream& os, pair<S,T> st){ os << "(" << st.first << "," << st.second <<")"; return os; }

typedef vector<int> vint;
typedef vector<ll> vll;
typedef vector<ul> vul;
typedef vector<ull> vull;
typedef vector<bool> vbl;
typedef pair<int, int> pii;

typedef complex<long long> Point;
istream& operator>>(istream& is, Point &pt){
    double a, b;
    is >> a >> b;
    pt.real(a * 1000000); pt.imag(b* 1000000);
    return is;
}

ostream& operator<<(ostream& os, const Point &pt){
    os << make_pair(pt.real(), pt.imag());
    return os;
}

inline long long cross(const Point &a, const Point &b){
    return (a.real()*b.imag() - a.imag()*b.real());
}

int main(void){

    int n;
    cin >> n;
    while(n-->0){
        Point a,b,c,d;
        cin >> a >> b >> c >> d;
//      DBG4(a, b, c, d);
//      DBG(cross(b - a, d - c));
        if(cross(b - a, d - c) == 0)
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }
    return 0;
}

C++: #include<iostream>
using namespace std;
main(){
  int n;
  double xa,ya,xb,yb,xc,yc,xd,yd,a2,a1;
  cin>>n;
  for(int i=0;i<n;i++){
    cin>>xa>>ya>>xb>>yb>>xc>>yc>>xd>>yd;
    a1=(yb-ya)/(xb-xa);
    a2=(yd-yc)/(xd-xc);
    if(a1==a2)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
}

C++: #include <iostream>

using namespace std;

typedef struct myvector{
  double x;
  double y;
}Vector;

Vector sub_vector(Vector& a, Vector& b)
{
  Vector ret;
  ret.x = b.x - a.x;
  ret.y = b.y - a.y;
  return ret;
}

double cross_product(Vector& a, Vector& b)
{
  return a.x * b.y - b.x * a.y;
}

int main()
{
  int n;
  cin >> n;
  for(int i = 0; i < n; i++){
    Vector A, B, C, D;
    cin >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y >> D.x >> D.y;
    Vector AB = sub_vector(A, B);
    Vector CD = sub_vector(C, D);
    if(cross_product(AB, CD) * 10000 == 0)
      cout << "YES" << endl;
    else 
      cout << "NO" << endl;
  }
}

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

int main() {
    double n,xx[4],yy[4],x,y;
    cin >> n;
    for(int i=0;i<n;i++){
        for(int j=0;j<4;j++) cin>>xx[j]>>yy[j];
        x=(yy[1]-yy[0])/(xx[1]-xx[0]),y=(yy[3]-yy[2])/(xx[3]-xx[2]);
        if(x==y)cout << "YES";
        else cout << "NO";
        cout << endl;
    }
}

C++: #include<stdio.h>

int main(void)
{
	double x[4]={0},y[4]={0},x1,x2,y1,y2;
	int i;
	scanf("%d",&i);

	while(i!=0)
	{
		scanf("%f %f %f %f %f %f %f %f",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2],&x[3],&y[3]);
		x1 = x[1]-x[0];   y1 = y[1]-y[0];
		x2 = x[3]-x[2];   y2 = y[3]-y[2];
		if(x1==0 && x2==0)
			printf("YES\n");
		else if((x1==0 && x2!=0) ||(x1!=0&& x2==0))
			printf("NO\n");
		else if(y1/x1 == y2/x2)
			printf("YES\n");
		else 
			printf("NO\n");

		i-=1;
	}
 return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <iostream>


using namespace std;

int main()
{
	int n;
	scanf("%d", &n);
	for (int i = 0; i < n; ++i)
	{
		double x[4], y[4];
		for (int j = 0; j < 4; ++j)
			scanf("%lf %lf", x+j, y+j);
		if (abs(atan((y[1]-y[0])/(x[1]-x[0])) - atan((y[3]-y[2])/(x[3]-x[2]))) < 3.14/1000)
			puts("YES");
		else
			puts("NO");
	}

	return 0;
}

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

int main(void) {
    int n;
    cin >> n;
    for(int i = 0; i < n; i++){
        double point[4][2];
        for(int j = 0; j < 4; j++){
            for(int k = 0; k < 2; k++){
                cin >> point[j][k];
            }
        }
        if(((point[1][0] - point[0][0]) / (point[1][1] - point[0][1])) == ((point[3][0] - point[2][0]) / (point[3][1] - point[2][1]))){
            cout << "Yes" << endl;
        }
        else{
            cout << "No" << endl;
        }
    }
}

C++: #include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <climits>
#include <cfloat>
using namespace std;

int main()
{
    int n;
    cin >> n;
    while(n-- > 0){
        vector<double> x(4), y(4);
        for(int i=0; i<4; ++i)
            cin >> x[i] >> y[i];
        if(fabs((y[1]-y[0]) * (x[3]-x[2]) - (y[3]-y[2]) * (x[1]-x[0])) < 1.0e-10)
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }
    return 0;
}