How to convert char[] to int with fail\success control?
It isn't doable, reliably, with the given specs. If the array has garbage in it, it won't necessarily fail to parse as an int. That said, you can try to parse as an int with atoi() or sscanf(), as suggested in the comments, and report that it did or did not parse, but not necessarily whether it is valid in some respect.

If you're in control of the array, zero its first element. Then if you get back a non-empty string, at least you'll know some command parameter had been placed in it.