Could $res%1 not give zero? Resulting in the +1 simply incrementing by one instead of rounding up?

dont use strcat() on uninitialized memory (e.g. that returned by malloc())

My bad code, Although A x B == B x A, so I'm not sure that it matters all that much.

OK, sorry for that.

Remember to mark as spoiler next time.

Но ведь js поддерживает индексацию с конца.
arr = [3, 2, 3]
arr[-1] === arr[0] // 3 = 3
sometimes it return error or not?

It does, but javascript will return "undefined" for out-of-bounds errors instead of crashing, so it works anyway.

Do we have to round available money reminder up to NEXT integer?
I can't understand how +0.5 works. It looks like this statement
will always round a number up to next int.

wow

At least, I've managed to grasp the main solution idea.

Production code is boring.

You can check out my 2 and 1 Kyu C translations though. I made about 50% of all of them.

I'm curious to look at your production code.