"*stringPtr++"

Why are you dereferencing the pointer in the for loop when you want just to increment it?

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'