woohoo

cool recursion worth my learning

It does the trick but there are some really concise solutions here with a fraction of the upvotes...

learnes a big lesson

Nice way to evaluate the arr is not empty or None.

L comment I won't lie

everything was much easier than I thought at first

It can also be None according to the kata description, which would then return None and fail.

Hey, I am still learning c and was wondering if you could use sprintf instead?

Ha, didn't know about asprintf(), and overlooked it when looking at snprintf() manpage, thanks!

Old comment, but if someone runs into a similar issue - are you returning an array of the values or just the values?

My first attempt returned 10,-65 instead of [10,-65] for the first example problem, which fails.

It is actually a very good solution because asprintf stops potential buffer overflowes.
Further read: https://stackoverflow.com/questions/12746885/why-use-asprintf-instead-of-sprintf

in the ASCII table you will find '\0' is equal to the demical '0'.
*buffer = 0; is equivalent to *buffer = '\0'

Oh not bad using if not
I never thought we could do that