You are changing the array and using the changed value to count the number. Do not store the output in the array you are using to count the length: 
#!/usr/bin/perl
use warnings;
use strict;

my @array = ('Hello, my name is John',
             'How are you?',
             'blah (blah)',
            );

my $count = 0;
for my $string (@array) {
    printf "%08d %s\n", $count, $string;
    $count += length $string;
}

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: Calculating/adding byte counts of array elements by choroba
in thread Calculating/adding byte counts of array elements by Dr Manhattan

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