Some code would have been nice, but you can try push( @c, shift(@a) - shift(@b)) while (@a and @b); It is destructive, but @c will contain the results when it is done and it.

or a non-descructive version  $c[$_] =  $a[$_] - $b[$_] for  0 ..  ($#a <  $#b ? $#a : $#b);, but I think the first is easier to read. ;)

Updated thanks to some comments from ysth regarding precedence and a typo )