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;
double x[4], y[4], xp[2], yp[2]; int n;
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 4; j++) { cin >> x[i] >> y[i]; }
		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() {
  int n;
  double x1, y1, x2, y2, x3, y3, x4, y4;
  double d1, d2;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    d1 = (y2 - y1) / (x2 - x1);
    d2 = (y4 - y3) / (x4 - x3);
    if (d1 == d2) {
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
  }
}

C++: #include <iostream>
#include <stdio.h>
#include <string>
#include <math.h>
#include <algorithm>
#include <vector>

using namespace std;
int main(){
	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)*(y4 - y3) == (x4 - x3)*(y2 - y1)){
			cout << "YES" << endl;
		}
		else{
			cout << "NO" << endl;
		}

	}
	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){
        ll x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = x_*100000 + 1e-9;
                y[i][j] = y_*100000 + 1e-9;
            }
        }
        ll dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        ll dx2=x[1][0]-x[1][1], dy2=y[1][0]-y[1][1];
        dump(dx1,dx2,dy1,dy2);
        puts(dx1*dy2==dx2*dy1 ? "YES" : "NO");
    }
}

C++: #include<stdio.h>
int main(void){
	int i, n;
	scanf("%d", &n);
	for (i = 0; i < n; i++){
		double x1, y1, x2, y2, x3, y3, x4, y4, a;
		scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);
		a = (y2 - y1) / (x2 - x1)
		  - (y4 - y3) / (x4 - x3);
		if (-0.000001<=a && a<=0.000001){
		printf("YES\n");
		}
		else{
			printf("NO\n");
		}
	}
	return 0;
}

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

int main(){
	int num;
	double sx1,sy1,sx2,sy2;
	double ex1,ey1,ex2,ey2;
	cin>>num;
	for(int i=0;i<num;i++){
		cin>>sx1>>sy1>>sx2>>sy2>>ex1>>ey1>>ex2>>ey2;
		if( (sy2-sy1)/(sx2-sx1) == (ey2-ey1)/(ex2-ex1) ){
			cout<<"YES"<<endl;
		}else{ 
			cout<<"NO"<<endl;
		}

	}

}

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

int main(){
	int n;
	double x[4], y[4];
	cin >> n;
	while (n-- != 0){
		for (int i = 0; i < 4; i++)
			cin >> x[i] >> y[i];
		if ((x[0] - x[1]) / (y[0] - y[1]) == (x[2] - x[3]) / (y[2] - y[3]))
			puts("YES");
		else
			puts("NO");
	}
	return 0;
}

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)
	{
		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;
}