Why am i getting runtime error?

Question

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll t;
cin>>t;
while(t--)
{
ll n;
cin>>n;
ll a[n];
for(ll ch=0;ch<n;ch++)
{cin>>a[ch];}
vector<ll> v;
ll count=0;
ll dif=a[1]-a[0];
for(ll i=0;i<n-1;i++)
{
if(a[i+1]-a[i]==dif)
{ count++;}
else
{dif=a[i+1]-a[i];
v.push_back(count);
count=1;}
}
sort(v.begin(),v.end());
cout<<"Case #"<<t-(t-1)<<": "<<v[v.size()-1]+1<<endl;

}
return 0;
}`Preformatted text`

Answer 1

Ayush Pattnaik C++does not support dynamic raw arrays on the stack. Compiler must know the exactly size of array for memory allocation.
Simply change
ll a[n];
to
vector<ll> a(n);
can resolve it.

Edit: This could still cause seg fault in some cases, and ~ swim ~ had correct answer.

For example, consider case
1 2 3 will cause error;
and
1 2 4 6 8 will give incorrect answer 2, not 3.

Answer 2

Still getting the same error

Answer 3

what is the input and the error? Could you share it?

Answer 4

This is the first question of round e Google kickstart