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 <vector>
#include <iostream>
#include <complex>

#define fs first
#define sc second

using namespace std;

typedef double D;
typedef complex<D> P;
typedef pair<P, P> L;
const D EPS=1e-12;


namespace std{
  bool operator<(const P &a, const P &b){
    return real(a)==real(b)?imag(a)<imag(b):real(a)<real(b);
  }
}

D cross(P x, P y){return imag(conj(x)*y);}

bool para(L a, L b){return abs(cross(a.fs - a.sc, b.fs-b.sc))<EPS;}

int main(){
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    D x1, y1, x2, y2, x3, y3, x4, y4;
    cin >>  x1 >> y1 >> x2 >> y2 >>  x3>> y3>> x4>> y4;
    P A = P(x1, y1);
    P B = P(x2, y2);
    P C = P(x3, y3);
    P D = P(x4, y4);
    L AB = L(A, B);
    L CD = L(C, D);
    if(para(AB, CD)){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
  }
}

C++: #include <stdio.h>

int main(void)
{
  long double x1,y1,x2,y2,x3,y3,x4,y4;
  int i,n;
  int ans[10];

  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);
    if( (y2-y1)*(x4-x3) == (y4-y3)*(x2-x1) ){
      ans[i] = 1;
    }else{
      ans[i] = 0;
    }
  }
  for(i=0;i<n;i++){
    if(ans[i] == 1){
      printf("YES\n");
    }else{
      printf("NO\n");
    }
  }
  return 0;
}

C++: #include <stdio.h>

#define ABS(X) ((X)<0 ? -(X) : (X))
int main(){
    int n;
    double x1, y1, x2, y2;
    double x3, y3, x4, y4;
    double dx1, dy1, dx2, dy2;
    
    scanf("%d", &n);
    for (int i=0; i<n; i++){
        scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
        scanf("%lf %lf %lf %lf", &x3, &y3, &x4, &y4);
        dx1 = x2 - x1;
        dy1 = y2 - y1;
        dx2 = x4 - x3;
        dy2 = y4 - y3;
        if (ABS(dx1*dy2 - dx2*dy1) < 0.0001){
            printf("YES\n");
        } else {
            printf("NO\n");
        }
    }

    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<map>
#include<complex>
#include<cstdlib>
#include<cstring>
#include<string>
#include<vector>
#include<functional>

using namespace std;

const double EPS=1e-12;
const double INF=1e12;

typedef complex<double>Point;

namespace std{
    bool operator<(const Point &P,const Point &Q){
        return real(P)!=real(Q)?real(P)<real(Q):imag(P)<imag(Q);
    }
}

double dot(const Point &P,const Point &Q){
    return real(P)*real(Q)+imag(P)*imag(Q);
}

double cross(const Point &P,const Point &Q){
    return real(P)*imag(Q)-real(Q)*imag(P);
}

struct Line{
    Point a,b;
    Line(Point P,Point Q){
        a=P;b=Q;
    }
    Line(){}
};

struct Segment{
    Point a,b;
    Segment(Point P,Point Q){
        a=P;b=Q;
    }
    Segment(){}
};

struct Circle{
    Point c;
    double r;
    Circle(Point P,double l){
        c=P;r=l;
    }
};

typedef vector<Point>Polygon;

int ccw(Point A,Point B,Point C){
    B-=A;C-=A;
    if(cross(B,C)>0)return 1; //ccw
    if(cross(B,C)<0)return -1; //cw
    if(dot(B,C)<0)return 2; //c-b-a
    if(norm(B)<norm(C))return -2; //a-b-c
    return 0; //a-c-b
}
inline bool Parallelism(const Line &L,const Line &M){
    return fabs(cross(L.a-L.b,M.a-M.b))<EPS;
}

inline bool Parallelism(const Segment &S,const Segment &T){
    return fabs(cross(S.a-S.b,T.a-T.b))<EPS;
}

inline bool intersect(const Line &L,const Line &M){
    return cross(L.a-L.b,M.a-M.b)>EPS ||cross(L.a-L.b,M.a-M.b)<-EPS;
}

inline bool intersect(const Line &L,const Segment &S){
    return cross(L.b-L.a,S.a-L.a)*cross(L.b-L.a,S.b-L.a)<-EPS;
}

inline bool intersect(const Line &L,const Point &P){
    return abs(ccw(L.a,L.b,P))!=1;
}

inline bool intersect(const Segment &S, const Segment &T){
    return ccw(S.a,S.b,T.a)*ccw(S.a,S.b,T.b)<=0&&
        ccw(T.a,T.b,S.a)*ccw(T.a,T.b,S.b) <= 0;
}

inline bool intersect(const Segment &S,const Point &P){
    return ccw(S.a,S.b,P)==0;
}

inline bool intersect(const Circle &C,const Point &P){
    return abs(C.c-P)<=C.r+EPS;
}

inline bool intersect(const Circle &C,const Circle &D){
    return abs(C.c-D.c)<=C.r+D.r&&abs(C.c-D.c)>=fabs(C.r-D.r);
}

inline Point crossPoint(const Line &L,const Line &M){

}
double areaTriangle(Point A,Point B,Point C){
    B-=A;C-=A;
    return fabs(cross(B,C))*0.5;
}

double areaPolygon(Polygon &g){
    const int Sz=g.size();
    if(Sz<3)return 0;
    if(Sz==3)return areaTriangle(g[0],g[1],g[2]);

    double res=cross(g[Sz-1],g[0]);
    for(int i=1;i<Sz;i++)res+=cross(g[i-1],g[i]);

    return fabs(res)*0.5;
}



int main(){
    int N;
    Line L,M;
    cin>>N;
    while(N--){
        cin>>L.a.real()>>L.a.imag()>>L.b.real()>>L.b.imag();
        cin>>M.a.real()>>M.a.imag()>>M.b.real()>>M.b.imag();
        if(Parallelism(L,M))cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
    }
    return 0;
}

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

#define rep(x,to) for(int x=0;x<to;x++)
#define rep2(x,from,to) for(x=from;x<to;x++)

using namespace std;


int main(void){

int N;
double x[4], y[4];

	cin >> N;
	while( N--){
		rep(i,4) cin >> x[i] >> y[i];
		
		if((y[1]-y[0])*(x[3]-x[2]) == (y[3]-y[2])*(x[1]-x[0])) 
  	    	cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}

C++: #include <vector>
#include <iostream>
#include <utility>
#include <algorithm>
#include <string>
#include <deque>
#include <queue>
#include <tuple>
#include <queue>
#include <functional>
#include <cmath>
#include <iomanip>
#include <map>
#include <set>
#include <numeric>
#include <unordered_map>
#include <unordered_set>
#include <complex>
#include <iterator>
#include <array>
#include <memory>
#include <stack>
#define vi vector<int>
#define vvi vector<vector<int> >
#define ll long long int
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vb vector<bool>
#define vc vector<char>
#define vs vector<string>
#define ld long double
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define loop(i,s,n) for(int i=s;i<n;i++)
#define all(in) in.begin(), in.end()
template<class T, class S> void cmin(T &a, const S &b) { if (a > b)a = b; }
template<class T, class S> void cmax(T &a, const S &b) { if (a < b)a = b; }
#define MAX 9999999
using namespace std;
typedef pair<int, int> pii;
typedef pair<double,double>pdd;
typedef pair<ll,ll>pll;
int main(){
    int n; cin>>n;
    rep(i,n){
    pdd a,b,c,d; cin>>a.first>>a.second>>b.first>>b.second;
    cin>>c.first>>c.second>>d.first>>d.second;
    if(abs((c.first-d.first)*(a.second-b.second)-(a.first-b.first)*(c.second-d.second))<=EPS)
        cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    }
}

C++: #include<cstdio>
#include<cmath>
#include<iostream>
#include<algorithm>
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(fabs((y2-y1)/(x2-x1)-(y4-y3)/(x4-x3))<0.0000001)cout<<"YES"<<endl;
		else cout<<"NO"<<endl;
	}
	return 0;
}

C++: #include<iostream>
using namespace std;
int main(){
  int n;
  double x1,y1,x2,y2,x3,y3,x4,y4,lI,lII;
  cin >> n;
  while(n--){
    cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
    cout << ((y2-y1)/(x2-x1) == (y4-y3)/(x4-x3) ? "YES" : "NO") << endl;
  }
}