Go: package main

import "fmt"

func abs(x float64) float64 {
	if x < 0 {
		return -x
	}
	return x
}

func main() {
	var n int
	var x1, y1, x2, y2, x3, y3, x4, y4 float64
	fmt.Scan(&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)
		if abs((x2-x1)*(y4-y3) - (y2-y1)*(x4-x3)) < 1e-10 {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

C++: #include <iostream>
using namespace std;
int main() {
  int n;
  cin >> n;
  for(int i = 0; i < n; ++i) {
    double x1, x2, x3, x4;
    double y1, y2, y3, y4;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    double dx1 = x1 - x2;
    double dy1 = y1 - y2;
    double dx2 = x3 - x4;
    double dy2 = y3 - y4;
    if(dx1 == 0 && dx2 == 0) {
      cout << "YES" << endl;
    } else {
    if(dy1 / dx1 == dy2 / dx2) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
    }
  }
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <string>
#include <math.h>
#include <functional>
#include <algorithm>

typedef long long Int;
#define REP(i,n) for(int i = 0 ; i < n ; ++i)
using namespace std;

int main(){
	double p[8];
	int n;
	cin >> n;

	REP(i, n){

		REP(i, 8){
			cin >> p[i];
		}

		string ans = abs((p[3] - p[1])*(p[6] - p[4]) - (p[7] - p[5])*(p[2] - p[0])) <= 0.0000005 ? "YES" : "NO";


		cout << ans << endl;
	}
	return 0;
}

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

using namespace std;

int main(int argc, char* argv[])
{
	double x1, y1, x2, y2, x3, y3, x4, y4;
	int tendAB, tendCD;
	int num;

	cin >> num;
	while (num--) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		tendAB = (y1 == y2) ? 0 : (x2 - x1) * 100000 / (y2 - y1);
		tendCD = (y3 == y4) ? 0 : (x4 - x3) * 100000 / (y4 - y3);
		if (tendAB == tendCD) cout << "YES" << endl; else cout << "NO" << endl;
	}

	return 0;
}

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

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

  for(int i=0;i<n;i++){
    complex<long double> v[4];
    for(int j=0;j<4;j++){
      long double x,y;
      cin >> x >> y;
      v[j]=complex<long double>(x,y);
    }

    if((conj(v[1]-v[0])*(v[3]-v[2])).imag()==0.0)
      cout << "YES" << endl;
    else
      cout << "NO" << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>
#include <sstream>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <numeric>
#include <cmath>
#include <climits>
#include <limits>
#include <cfloat>
#include <fstream>
using namespace std;

int main()
{
//	cut here before submit 
//	freopen("testcase.pl", "r", stdin);
	string str = "";
	int n;

	getline (cin, str );
	stringstream ssn(str);
	ssn >> n;

	int i,j;
	for (i = 0; i < n; ++i){
		vector <double> px (4, 0.0);
		vector <double> py (4, 0.0);
		getline (cin, str );
		stringstream ss(str);
		for (j = 0; j < 4; ++j){
			ss >> px[j] >> py[j];
		} // end for
		map <double, double> v;

		for (j = 0; j < 2; ++j){
			v[px[2*j + 1] - px[2*j]] = py[2*j + 1] - py[2*j];
		} // end for
		if (v.size() == 1){
			cout << "YES" << endl;
			continue;
		} // end if
		map <double, double>::iterator it = v.begin();
		double x = (*it).first;
		double y = (*it).second;
		++it;
		if ((*it).first/x == (*it).second/y){
			cout << "YES" << endl;
		}else{
			cout << "NO" << endl;
		} // end if
	} // end for
		
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
const double eps = 1e-6;

int main() {
    int n;
    double x1, y1, x2, y2, x3, y3, x4, y4;
    cin >> n;
    while(n--) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
        cout << (fabs((x2-x1)*(y4-y3) - (x4-x3)*(y2-y1)) < eps ? "YES" : "NO") << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<cmath>
#include<algorithm>
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,a) loop(i,0,a)
using namespace std;

int main(){
	int n;
	pair<double,double> p[4],vec[2];
	cin>>n;
	rep(j,n){
		rep(i,4)cin>>p[i].first>>p[i].second;
		rep(i,2){
			vec[i].first=p[i*2].first-p[i*2+1].first;
			vec[i].second=p[i*2].second-p[i*2+1].second;
		}
		double check=vec[0].first*vec[1].second-vec[0].second*vec[1].first;
		if(abs(check)<1e-6)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
using namespace std;
int main() {
	int n;
	cin >> n;
	for (int z = 0; z < n; z++) {
		long float x1, x2, x3,y1, y2, y3, y4, x4 ;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
		if (y1 > y2) {
			swap(y1, y2);
			swap(x1, x2);
		}
		if (y3 > y4) {
			swap(y3, y4);
			swap(x3, x4);
		}
		if ((x1 > x2&&x3 > x4 && ((y2 - y1) / (x1 - x2) == (y4 - y3) / (x3 - x4))) || (x2 > x1&&x4 > x3 && ((y1 - y2) / (x2 - x1) == (y3 - y4) / (x4 - x3)))) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}

C++: #include <iostream>
using namespace std;
int main(){
  
  double x1, y1, x2, y2, x3, y3, x4, y4;
  int dataSets;
  cin >> dataSets;
  for(int i=0;i<dataSets;i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> x4 >> y4;
    if((y2-y1)*(x4-x3) - (x2-x1)*(y4-y3) == 0.0){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
    
  }

  return 0;

}

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

const double EPS = 1e-10;

signed main() {
  int n;

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

  return 0;
}

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

using namespace std;

struct Point {
    double x, y;
};

int main() {
    int n;
    cin >> n;
    while (n--) {
        Point p[4];
        for (int i = 0; i < 4; i++) {
            cin >> p[i].x >> p[i].y;
        }
        double div1 = (p[1].x - p[0].x) / (p[3].x - p[2].x);
        double div2 = (p[1].y - p[0].y) / (p[3].y - p[2].y);
        if (div1 == div2) {
            cout << "YES\n";
        }
        else {
            cout << "NO\n";
        }
    }
    
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

int main()
{
  int n;
  cin >> n;
  while (n--){
    double x[4], y[4];
    bool f = false;
    for (int i = 0; i < 4; i++) cin >> x[i] >> y[i];
    if (x[0] - x[1] == x[2] - x[3] && y[0] - y[1] == y[2] - y[3]){
      f = true;
    }

    if (f){
      cout << "YES\n";
    }
    else {
      cout << "NO\n";
    }
  }
}

C++: #include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<sstream>
#include<algorithm>
#include<cmath>
#include<map>
#include<functional>
#include<queue>
#include<stack>
#include<set>
#include<math.h>
using namespace std;
#define SZ(n)  (int)n.size()
#define dump(x) cerr<<#x<<" = "<<(x)<<endl;
#define debug(x)cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define MP make_pair
#define PB push_back
	double EPS=1e-10;
	bool same(double a,double b){
		if(fabs(a-b)<=EPS)return 1;
		else return 0;
	}
	
	
	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;
		double a1=(y1-y2)/(x1-x2);
		double a2=(y3-y4)/(x3-x4);
		if(same(a1,a2))cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	
	return 0;
}