Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"fmt"
	"strings"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextInt() int {
	scanner.Scan()
	i, e := strconv.Atoi(scanner.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func main() {
	n := nextInt()
	for i := 0; i < n; i++ {
		scanner.Scan()
		points := strings.Split(scanner.Text(), " ")
		fpoints := make([]float64, 0)
		for _, v := range points {
			tmp, _ := strconv.ParseFloat(v, 64)
			fpoints = append(fpoints, tmp)
		}
		a := (fpoints[1]-fpoints[3])/(fpoints[0]-fpoints[2])
		b := (fpoints[5]-fpoints[7])/(fpoints[4]-fpoints[6])
		if a == b {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

C++: #include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <ctime>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <set>
#include <map>
#include <iostream>
#include <deque>
#include <complex>
#include <string>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <valarray>
#include <iterator>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) container.begin(), container.end()
#define RALL(container) container.rbegin(), container.rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-10;
const int MOD = 1000000007;

#define X real()
#define Y imag()

typedef complex<double> P;
struct L{
	P p1, p2;
	L(P p1, P p2):p1(p1), p2(p2){}
	L(){}
};
istream& operator>>(istream &is, P &p) {
	double x, y;
	is >> x >> y;
	p = P(x, y);
	return is;
}
inline int sig(double x) { return (abs(x) < EPS ? 0 : x > 0 ? 1 : -1); }
inline double norm(const P &p){return p.X*p.X+p.Y*p.Y;}
inline double inp(const P& a, const P& b){return (conj(a)*b).X;}
inline double outp(const P& a, const P& b){return (conj(a)*b).Y;}


int T;

int main(){
	ios::sync_with_stdio(false);
	cin >> T;
	while(T--){
		P p1, p2, p3, p4;
		cin >> p1 >> p2 >> p3 >> p4;
		puts(!sig(inp(p2-p1, (p4-p3)*P(0., 1.))) ? "YES" : "NO");
	}
	return 0;
}

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

int main() {
	int N;
	double x[4],y[4];
	cin>>N;
	while(N--){
		for(int i=0;i<4;i++) cin>>x[i]>>y[i];
		double y1=y[1]-y[0];
		double x1=x[1]-x[0];
		double y2=y[3]-y[2];
		double x2=x[3]-x[2];
		if(y1*x2==y2*x1) cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

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

int main()
{
	int num ;
	double ax, ay, bx, by, cx, cy, dx, dy ;

	cin >> num ;
	for( int i = 0 ; i < num ; i ++ )
	{
		cin >> ax >> ay >> bx >> by >> cx >> cy >> dx >> dy ;

		if( ((by-ay)/(bx-ax)) == ((dy-cy)/(dx-cx)) ) cout << "YES\n" ;
		else cout << "NO\n" ;
	}
	return 0;
}

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

C++: #include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
#define EPS 1e-9

int main(){
  int n;
  double ab,cd;
  double x1,y1,x2,y2,x3,y3,x4,y4;

  scanf("%d", &n);
  while(n--){
    scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);

    if(x2 == x1){
      if(x3 == x4) printf("YES\n");
      else printf("NO\n");
      continue;
    }
    ab = (y2-y1) / (x2-x1);
    cd = (y4-y3) / (x4-x3);

    if(fabs(ab - cd) < EPS) printf("YES\n");
    else printf("NO\n");
  }

  return 0;
}

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=0.00000000000000001;
	bool same(double a,double b){
		if(fabs(a-b)<=EPS)return 1;
		else return 0;
	}
	
	
	int main(){
	int n;
			double x1,y1,x2,y2,x3,y3,x4,y4,a1,a2;
	cin>>n;
	for(int i=0;i<n;i++){

		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		a1=(y1-y2)/(x1-x2);
		a2=(y3-y4)/(x3-x4);
		if(same(a1,a2))cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	
	return 0;
}

C++: #include <stdio.h>

int main(void){
	int n, i;
	double x1,x2,x3,x4,y1,y2,y3,y4;
	scanf("%d",&n);
	for(i = 0;i < n;i++){
		scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
		double out = ((x2 - x1) * (y4 - y3)) - ((y2 - y1) * (x4 - x3));
		if(out == 0){
			printf("YES\n");
		}else{
			printf("NO\n");
		}
	}
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <numeric>
#include <string>
#include <vector>
#include <list>
#include <iterator>

#include <cmath>

typedef std::pair<double,double> Vec;
typedef std::pair<Vec,Vec> Line;

Vec operator+(const Vec& lhs, const Vec& rhs) {
	return std::make_pair(lhs.first+rhs.first, lhs.second+rhs.second);
}

Vec operator-(const Vec& lhs, const Vec& rhs) {
	return std::make_pair(lhs.first-rhs.first, lhs.second-rhs.second);
}

Vec lineToVec(const Line& l) {
	return l.first - l.second;
}

double cross(const Vec& lhs, const Vec& rhs) {
  return lhs.first*rhs.second - lhs.second*rhs.first;
}

int main(void){
	using namespace std;

	int n;
	cin >> n;

	vector< pair<Line,Line> > input;
	input.reserve(n);

	for(int i=1; i<=n; i++){
		double x1,y1,x2,y2,x3,y3,x4,y4;
		cin
			>> x1 >> y1
			>> x2 >> y2
			>> x3 >> y3
			>> x4 >> y4;

		auto AB = make_pair( make_pair(x1,y1), make_pair(x2,y2) );
		auto CD = make_pair( make_pair(x3,y3), make_pair(x4,y4) );

		input.push_back(make_pair(AB,CD));
	}

	for(auto itr=input.begin(); itr!=input.end(); itr++){
		auto AB = itr->first;
		auto CD = itr->second;

		auto cr = cross( lineToVec(AB), lineToVec(CD) );

		if( abs(cr) <1e-10 ){
			cout << "YES";
		}
		else{
			cout << "NO";
		}
		if( distance( itr, input.end() )>0 ){
			cout << endl;
		}
	}
}