Why am I getting a runtime error on codechef, but not on sololearn?

Question

The program is about merging 2 arrays in C.
If some changes are to be made to the code, then please suggest.

https://code.sololearn.com/cXr5D2rDqL5m/#c

Answer 1

No, I got my mistake, it was due to void main.
If we use int main, then it gets successfully compiled. I'm just wondering what would be the reason behind this...

Answer 2

Codechef is online judge, online judge never ask for printing text like “input size array”, instead just scanf instantly.
this might be the cause

Answer 3

Of course, compiler.