Oh, very good. It failed, expected 7 submitted 8. And I see where my code is wrong, too. And it really wouldn't happen very often in random test cases.
I've re-submitted my code with correction, and will be marking this resolved, but think that it should be added to the edge cases to have it come up each time and not just randomly during that test phase.

This solution is not 100% good, since it fails on some edge cases that only popped up occasionally during the Attempts, and I was unable to debug because of the inconsistency of them showing up.
This has been corrected in my second submission.

@hobovsky: you should be able to see my submitted "solution" by clicking the 'View Solution' underneath my comment.

I'm just wondering if it couldn't come from how I handle 0.

My C solution could pass or fail the random tests, without being modified between attempts. Thoughts?

I'm having an STRERR message when I attempt to run my code (tests run fine):
free(): invalid next size (fast)

I believe there may be an error in the line for the C tests, for strin="nine", n=9.

I'm getting the following strerr message when I attempt my C code (tests run fine):
free(): invalid next size (fast)

I believe there is an issue with the C test code, as I use a calloc, and it works fine in the preceding cases. It seems to fail on the test strin="nine", n=9.