Thank you very much for the detailed answer.

Thanks!

Can someome please explain me why cant I do the assignment like this : ans[i] = str[i]; ?
Thanx

Clever use of qsort. I asked myself how to sort the ints like this with a single compare function. Thank you for the example. Maybe returning *a -*b or *b - *a could produce some overflows.

nah, I think it's to give extra space in case of memory overflow

This is absolutely NOT "best practice", nor is it clever, as it's modifying a const string it will typically crash.

Really? https://stackoverflow.com/questions/4774456/pass-an-array-to-a-function-by-value

it crashes when you run it against the sample tests (button TEST), and passes when you run it against the full tests (button ATTEMPT). The sample and full tests are independent (they are in separate files).

• The sample tests are the ones you can see on the Trainer page; they are only here so that you can get an idea of how your solution is called and which kind of inputs you can expect.
• The full tests suite (which you cannot see unless you completed the kata) are used to determine whether your solution is correct or not. It does not matter if you pass the sample tests or not to complete a kata.

usually, the sample tests are also copied to the full tests suite, but this is just a convention and authors can write tests differently. In this particular kata, the author of the C version did not do this: the sample tests call the user function with read-only string literals (which crashes this solution), but the full tests call it with mutable strings, so this solution can get away with removing const

i think int a[] is a copy of array, so sorting it have no problem.