for(my $iSheet=0; $iSheet < $oBook->{SheetCount}; $iSheet++)
    {
        print "$oBook->{SheetCount}";
    }

##</code><code>##

use strict;
use warnings;
use Benchmark qw/ timethese cmpthese /;

my $oBook = { SheetCount => 1000 };

cmpthese(timethese(10000, {
        'For_C'   => '&For_C',
        'For_Set' => '&For_Set',
    }));

sub For_C
{
    my $var;
    for (my $iSheet=0;
         $iSheet < $oBook->{SheetCount};
         $iSheet++)
    {
        $var = $iSheet;
    }
}

sub For_Set
{
    my $var;
    for my $iSheet (0..$oBook->{SheetCount}-1)
    {
        $var = $iSheet;
    }
}

##</code><code>##

Benchmark: timing 10000 iterations of For_C, For_Set...
     For_C: 14 wallclock secs (14.33 CPU) @ 697.84/s (n=10000)
   For_Set:  7 wallclock secs (7.22 CPU) @ 1385.04/s (n=10000)
          Rate   For_C For_Set
For_C    698/s      --    -50%
For_Set 1385/s     98%      --

##</code><code>##

$iSheet < $oBook->{SheetCount} # hash look up and comparison