$a is definitely going beyond the end of @hfr. Use < instead of <= in the loop test to avoid this.

Oh, and don't use $a as a variable name. Nor $b for that matter.

Update: For some reason I had missed that Cristoforo had already mentioned this. Sorry for the waste of bandwidth.

In reply to Re^2: use of uninitialized value in array by hippo
in thread use of uninitialized value in array by rocketperl

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