I can't understand from editorial or any of the comments.Thanks in advance.

This code gives runtime error.

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll maxc = 1e6+10;
ll bit[maxc];

ll n;

int main()
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ll a[maxc] , u[maxc] , q[maxc];
  //some stuff with the arrays
  return 0;
}

And this works fine.

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll maxc = 1e6+10;
ll bit[maxc];
ll a[maxc] , u[maxc] , q[maxc];

ll n;

int main()
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  //some stuff with the arrays
  return 0;
}

Can anyone tell me why??

I want to reuse it . How am I supposed to do it?