A few C functions I need help with

These are pretty trivial, but I am no programmer.


if I do swap( 4, 6 )

where

int swap( int x, int y) {
   x = y;
   y = x;
   return( y );
}

What will it return and why?

Thank you for the explanation and I am especially grateful for the improved version.

Since there is int before swap, the returned 6 would be considered integer, correct?

What purpose does the void type serve in the improved (and also working) version of swap?

Now, onto the next one:

int excl( int n ) {
  if ( n == 1 ) return 1;
  return n * excl( n - 1 );
}

I'm pretty sure this is just a function to compute factorial. The problem is what happens, when 0 (or negative number) is on the input. Will it result in an infinite loop? If so, how to prevent this and make it correctly output excl(0) as 1?