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 <iostream>
using namespace std;

int main() {
double x1,x2,x3,x4,y1,y2,y3,y4;
int n;
cin>>n;
for(int jjj=1;jjj<=n;jjj++){
	cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
	if(x1==x2||x3==x4){
		if(x3==x4&&x1==x2){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}}
	else{
		double k=(y2-y1)/(x2-x1),l=(y4-y3)/(x4-x3);
		if(k==l){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}
	}	
	}

	return 0;
}

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

using namespace std;

int main() {
	int k;
	double x1,x2,x3,x4,y1,y2,y3,y4;
	double katamuki1;
	double katamuki2;
	cin >> k;

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

		katamuki1 = (y2 - y1) / (x2 - x1);
		katamuki2 = (y4 - y3) / (x4 - x3);

		if (katamuki1 == katamuki2) {
			if(((y4 - y1) / (x4 - x1)) == ((y3 - y2) / (x3 - x2))) {
				cout << "NO" << endl;
			} else {
				cout << "YES" << endl;
			}
		} else {
			cout << "NO" << endl;
		}
	}
	return 0;
}

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

using namespace std;

typedef struct _POINT {
	double x;
	double y;
} POINT;

typedef struct _LINE {
	POINT a;
	POINT b;
} LINE;

bool isParallel (LINE l1, LINE l2) {
	double f1 = l1.b.x - l1.a.x;
	double g1 = l1.b.y - l1.a.y;
	double f2 = l2.b.x - l2.a.x;
	double g2 = l2.b.y - l2.a.y;

	return (fabs(f2*g1 - f1*g2) < 0.00001);
/*
	double det = f2*g1 - f1*g2;
	if (det == 0.0)
		return true;
	else
		return false;
*/
}

int main() {
	LINE ab, cd;
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> ab.a.x >> ab.a.y >> ab.b.x >> ab.b.y >> cd.a.x >> cd.a.y >> cd.b.x >> cd.b.y;
		if (isParallel(ab, cd))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}

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

using namespace std;

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

  cin>>n;

  for(i=0;i<n;i++)
    {
      cin>>x>>y>>x1>>y1;
      if(x1-x!=0.0)
	{
          a=(y1-y)/(x1-x);
          j++;
	}
      else
        k++;

      cin>>x>>y>>x1>>y1;
      if(x1-x!=0.0)
	{
          b=(y1-y)/(x1-x);
          j++;
	}
      else
        k++;

      if((a==b && j==2) || k==2)
        puts("YES");
      else
        puts("NO");
    }

}

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;
		double dx1 = x2-x1,
			   dy1 = y2-y1,
			   dx2 = x4-x3,
			   dy2 = y4-y3;
		
		if (dx2 * dy1 == dx1 * dy2) {
			if (dx1*dy1*dx2*dy2 != 0.0) {
				cout << "YES" << endl;
			} else {
				if (dx2+dy2 == 0.0 || dx1+dy1 == 0.0) {
					cout << "NO" << endl;
				} else {
					cout << "YES" << endl;
				}
			}
		} else {
			cout << "NO" << endl;
		}
	}
	return 0;
}

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

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

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

		a = (ay-by)/(ax-bx) ;
		b = (cy-dy)/(cx-dx) ;

		if( a == b )
		{
			cout << "YES" << endl ;
		}
		else
		{
			cout << "NO" << endl ;
		}
	}
	return 0 ;
}

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

}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <sstream>
#include <utility>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define each(e,c) for(auto&e:c)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define lb lower_bound
#define ub upper_bound
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<(DUMP(),__VA_ARGS__).str()<<" ["<<__LINE__<<"]"<<endl)
struct DUMP:ostringstream{template<class T>DUMP &operator,(const T&t){if(this->tellp())*this<<", ";*this<<t;return *this;}};
#else
#define dump(...)
#endif

int main(){
    int n; cin>>n;
    rep(_,n){
        ll x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = x_ *100000 + 0.5;
                y[i][j] = y_ *100000 + 0.5;
            }
        }
        ll dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        ll dx2=x[1][0]-x[1][1], dy2=y[1][0]-y[1][1];
        dump(dx1,dx2,dy1,dy2);
        puts(dx1*dy2==dx2*dy1 ? "YES" : "NO");
    }
}

C++: #include <iostream>

using namespace std;

int main(){
	int n;
	float x1,y1,x2,y2,x3,y3,x4,y4,s1,s2;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3>>x4>>y4;
		s1=(y2-y1)/(x2-x1);
		s2=(y4-y3)/(x4-x3);
		if(s1==s2){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;	
		}
	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
#include <string>
#include <map>
#include <functional>
#include <cmath>
#include <cstdio>
using namespace std;

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

C++: #include<stdio.h>

int main(void){
	double x[4],y[4];
	int n,i;
	
	scanf("%d",&n);
	
	for(i=0;i<n;i++){
		scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2],&x[3],&y[3]);
		
		if(((y[1]-y[0])/(x[1]-x[0])) == ((y[3]-y[2])/(x[3]-x[2])))printf("YES\n");
		else printf("NO\n");
	}
	
	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[0] - x[1]) / (y[0] - y[1]) == (x[2] - x[3]) / (y[2] - y[3]);
		if (h)
		{
			cout << "YES" << endl;
		}
		else
			cout << "NO" << endl;
	}




	return 0;
}