Try to replace all occurrences of $1 with $i. The problem occurs when assigning 0 to $1 in the for()-loop construct.

You cannot assign to $1 directly using the = operator - so from that point of view, $1 is read-only. $1 is usually set by a matching regular expression (capture), see also perlre.

Maybe, you should also increase your editors font size? ;-)

Update: Off-topic but maybe of interest: Announcing Source Code Pro