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 <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
#include <functional>
#include <sstream>
#include <utility>
#include <cstdlib>
#include <cctype>
#include <climits>
#include <fstream>

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<pair<int, int> > vpii;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) for(int i=0;i<(n);++i)
#define foreach(itr,c) for(__typeof(c.begin()) itr=c.begin(); itr!=c.end(); itr++)
#define dbg(x) cout << #x"="<< (x) << endl
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back(a) 
#define in(x) cin >> x;
#define all(x) (x).begin(), (x).end()
#define INF 2147483600
#define fi first
#define se second
using namespace std;

int main(){
	int N;
	vd a(8);
	cin >> N;
	rep(i,N){
		rep(i,8){
			cin>>a[i];
		}
		if(((a[1]-a[3])*(a[4]-a[6])-(a[5]-a[7])*(a[0]-a[2]))*((a[1]-a[3])*(a[4]-a[6])-(a[5]-a[7])*(a[0]-a[2]))<0.000001){
			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 xx,yy,EPS=1e-1;
    ll x[4],y[4];
    rep(i,4){
      cin>>xx>>yy;
      x[i]=xx*1e5+EPS;
      y[i]=yy*1e5+EPS;
      //   cout<<x[i]<<","<<y[i]<<endl;
    }cout<<1e5<<endl;
    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;
}

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

using namespace std;

void swap(double &x, double &y, double &xx, double &yy) 
{
  double tmp_x = x;
  double tmp_y = y;
  x = xx;
  y = yy;
  xx = tmp_x;
  yy = tmp_y;
}

void compute(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) 
{
  if (x1 > x2) swap(x1, y1, x2, y2);
  if (x3 > x4) swap(x3, y3, x4, y4);

  double diff_x12 = x2 - x1;
  double diff_y12 = y2 - y1;
  double diff_x34 = x4 - x3;
  double diff_y34 = y4 - y3;

  if (diff_x12 != 0 && diff_x34 != 0) {
    if (diff_y12 == 0.0 && diff_y34 == 0.0)
      cout << "YES" << endl;
    else {
      double ab = diff_y12 / diff_x12;
      double cd = diff_y34 / diff_x34;
      if (abs(ab - cd) < 0.00001)
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  else if (diff_x12 == 0.0 && diff_x34 == 0.0) {
    cout << "YES" << endl;  
  }
  else
    cout << "NO" << endl;  
}

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;
    compute(x1, y1, x2, y2, x3, y3, x4, y4);
  }
  
  return 0;
}

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

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		double x[4], y[4];
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

		bool h = (x[2] - x[3]) * (y[0] - y[1]) == (x[0] - x[1]) * (y[2] - y[3]);
		if (h)
		{
			cout << "YES" << endl;
		}
		else
			cout << "NO" << endl;
	}




	return 0;
}

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 ){
        loop:
        if( n == 0 ) break;
        scanf("%lf %lf %lf %lf %lf %lf %lf %lf %lf\n", &x1, &y1, &y2, &y2, &y3, &y3, &y4, &y4 );
        double num1 = x2 - x1, num2 = x4 - x3, num3 = y2 - y1, num4 = y4 - y3;
        if( (num1 == 0 && num3 == 0) || (num2 == 0 && num4 == 0 ) )
        {
            printf( "YES\n" );
            n--;
            goto loop;
        }
        else
        {
            num2 /= num1;
            num4 /= num3;
            if( num3 == num4 || num3 == -num4 )
            {
                printf( "YES\n" );
                n--;
                goto loop;
            }
        }
        printf( "NO\n" );
        n--;
    }
}

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

//const static double	de_PI	= 3.14159265358979323846;
//const static int	de_MOD	= 1000000007;
const static int	de_MAX	= 999999999;
//const static int	de_MIN = -999999999;

inline double RoundOff(double a, const int n) {

	for (int i = 0; i < n - 1; i++) { a *= 10; }

	if (a > 0) { a += 0.5; }
	else { a -= 0.5; }

	a = static_cast<int>(a);

	for (int i = 0; i < n - 1; i++) { a /= 10; }

	return a;
}

int main(void) {

	//std::ifstream in("123.txt");	std::cin.rdbuf(in.rdbuf());

	int n = 0;
	std::cin >> n;

	double x1 = 0, y1 = 0, x2 = 0, y2 = 0;
	double slope1 = 0, slope2 = 0;
	std::vector<std::string> ans(n);

	for (int i = 0; i < n; i++) {
		std::cin >> x1 >> y1 >> x2 >> y2;
		if (x1 == x2) {
			slope1 = de_MAX;
		}
		else if (y1 == y2) {
			slope1 = 0;
		}
		else {
			slope1 = RoundOff((y2 - y1) / (x2 - x1), 6);
		}

		std::cin >> x1 >> y1 >> x2 >> y2;
		if (x1 == x2) {
			slope1 = de_MAX;
		}
		else if (y1 == y2) {
			slope1 = 0;
		}
		else {
			slope2 = RoundOff((y2 - y1) / (x2 - x1), 6);
		}

		if (slope1 == slope2) {
			ans[i] = "YES";
		}
		else {
			ans[i] = "NO";
		}
	}

	for (int i = 0; i < n; i++) {
		std::cout << ans[i] << std::endl;
	}

}

C++: #include <iostream>
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((y2-y1)/(x2-x1) == (y4-y3)/(x4-x3)){
			cout << "YES" <<endl;
		}else{
			cout << "NO" <<endl;
		}
		
	}
	return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
bool EQ(double a,double b){
  return abs(a-b)<0.000000001;
  //  return a-0.0000001<b&&b<a+0.0000001;
}
int main(){
  int n;
  double x[4],y[4];
  cin>>n;
  while(n--){
    for(int j=0;j<4;j++) cin>>x[j]>>y[j];
    if(EQ((y[3]-y[2])*(x[1]-x[0]),(y[1]-y[0])*(x[3]-x[2])))cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
  return 0;
}