Sometimes the sized array form is actually never available, as with dynamically allocated memory. The correct pattern for all those cases is to pass around the size from where it's known, along with the pointer. One can also use a sentinel element to solve some problems without knowing the size explicitly.
Edit: The real point is, what was it about his answer that was hated/downvoted? Surely not the fact the sizeof(a)/sizeof(a[o]) requires a little knowledge and care?
Must be some sort of SO culture we're missing. Because in normal day-to-day conversation between reasonable adults, this would have been an acceptable answer.