That's a K&R (Kernighan and Ritchie) style function declaration. Compilers still support it but the version you'd be more familiar with (ANSI C style) has been standard since at least the late 80s IIRC. ANSI C was standardised in 1989 but that process had been in progress for something like 5 years beforehand.
Specifically, everything is an integer with the auto lifetime (gets discarded with the stack frame) unless otherwise specified.
I think most modern compilers will warn on encountering such short hand due to the common error of accidentally declaring integers when you meant to assign a value to a variable you forgot to declare.
