The first "$i" in the for loop causes the warning. "$i" at that point is a statement that does nothing and the resultant value is not used by anyone (normally an assignment occurs there) and hence the "useless use" warning.

This program will generate the same warning:

#!/usr/bin/perl
use strict;
use warnings;
my $y = 9;
$y;
exit 0;
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Change the for loop to

    for(;$i<$Size;$i++) {
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and the warning will go away.