Language: 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){
        double x[2][2], y[2][2];
        rep(i,2){
            rep(j,2){
                double x_,y_;
                cin >> x_ >> y_;
                x[i][j] = x_;
                y[i][j] = y_;
            }
        }
        double dx1=x[0][0]-x[0][1], dy1=y[0][0]-y[0][1];
        double 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");
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:18:25: error: 'll' was not declared in this scope; did you mean 'all'?
   18 | #define loop(i,a,b) for(ll i=a; i<ll(b); i++)
      |                         ^~
a.cc:19:18: note: in expansion of macro 'loop'
   19 | #define rep(i,b) loop(i,0,b)
      |                  ^~~~
a.cc:36:5: note: in expansion of macro 'rep'
   36 |     rep(_,n){
      |     ^~~
a.cc:36:9: error: '_' was not declared in this scope
   36 |     rep(_,n){
      |         ^
a.cc:18:33: note: in definition of macro 'loop'
   18 | #define loop(i,a,b) for(ll i=a; i<ll(b); i++)
      |                                 ^
a.cc:36:5: note: in expansion of macro 'rep'
   36 |     rep(_,n){
      |     ^~~
a.cc:38:13: error: expected ';' before 'i'
   38 |         rep(i,2){
      |             ^
a.cc:18:28: note: in definition of macro 'loop'
   18 | #define loop(i,a,b) for(ll i=a; i<ll(b); i++)
      |                            ^
a.cc:38:9: note: in expansion of macro 'rep'
   38 |         rep(i,2){
      |         ^~~
a.cc:38:13: error: 'i' was not declared in this scope
   38 |         rep(i,2){
      |             ^
a.cc:18:33: note: in definition of macro 'loop'
   18 | #define loop(i,a,b) for(ll i=a; i<ll(b); i++)
      |                                 ^
a.cc:38:9: note: in expansion of macro 'rep'
   38 |         rep(i,2){
      |         ^~~
a.cc:39:17: error: expected ';' before 'j'
   39 |             rep(j,2){
      |                 ^
a.cc:18:28: note: in definition of macro 'loop'
   18 | #define loop(i,a,b) for(ll i=a; i<ll(b); i++)
      |                            ^
a.cc:39:13: note: in expansion of macro 'rep'
   39 |             rep(j,2){
      |             ^~~
a.cc:39:17: error: 'j' was not declared in this scope
   39 |             rep(j,2){
      |                 ^
a.cc:18:33: note: in definition of macro 'loop'
   18 | #define loop(i,a,b) for(ll i=a; i<ll(b); i++)
      |                                 ^
a.cc:39:13: note: in expansion of macro 'rep'
   39 |             rep(j,2){
      |             ^~~