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 num;
  cin >> num;

  double x[4], y[4];
  double xx, yy;
  int i = 0;

  while( i < num ){
  for( int j = 0; j < 4; j++ ){
    cin >> x[j] >> y[j];
  }
  if((y[1]- y[0]) / (x[1] - x[0]) == (y[3] - y[2]) / (x[3] - x[2]) ){
    cout <<"YES"<< endl;
  }else{
    cout <<"NO"<< endl;
  }
  i++;
  }

 
  return 0;
}

C++: #include<iostream>
#include<queue>
#include<string>
#include<stack>
#include<cstdio>
#include<algorithm>

using namespace std;

int main(void)
{
  double x=0.0,y=0.0;
  double x1=0.0,y1=0.0;
  int n=0;
  int i=0;
  long double a,b;

  cin>>n;

  for(i=0;i<n;i++)
    {
      cin>>x>>y>>x1>>y1;
      a=(y1-y)/(x1-x);

      cin>>x>>y>>x1>>y1;
      b=(y1-y)/(x1-x);
	
      if(a==b)
        puts("YES");
      else
        puts("NO");
    }

}

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]))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}

C++: #include<iostream>

int main(){
  int n;
  double x1,y1,x2,y2,x3,y3,x4,y4;
  const double e = 1e-8;

  std::cin >> n;

  for(int i=0;i<n;i++){
    std::cin >> x1 >> y1
             >> x2 >> y2
             >> x3 >> y3
             >> x4 >> y4;

    if((x1*y3+x2*y4+y2*x3+y1*x4)-(x2*y3+x1*y4+y1*x3+y2*x4)<e){
      std::cout << "YES" << std::endl;
    }else{
      std::cout << "NO" << std::endl;
    }
  }
}

C++: //41
#include<iostream>
#include<complex>

using namespace std;

int main(){
  int n;
  cin>>n;
  for(int i=0;i<n;i++){
    complex<double> p[2];
    for(int j=0;j<2;j++){
      double x,xx,y,yy;
      cin>>x>>y>>xx>>yy;
      p[j]=complex<double>(x-xx,y-yy);
    }
    cout<<((p[0].real()*p[1].imag()-p[0].imag()*p[1].real())?"NO":"YES")<<endl;
  }
  return 0;
}

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;
}