Problem with that is the length is increasing as you insert commas from the right so it needs to be tested dynamically. Unfortunately, your modification breaks the routine.

use strict;
use warnings;

my @nos = qw{
   1
   12
   123
   1234
   12345
   123456
   1234567
   12345678
   123456789
   1234567890
   12345678901
   123456789012
   1234567890123
   12345678901234};

printf qq{%20s\n}, useSubstr($_) for @nos;

sub useSubstr
{
    my $number = shift;
    my $length = -( 1 + length $number );
    my $offset = -3;
    while ( $offset > $length )
    {
        substr $number, $offset, 0, q{,};
        $offset -= 4;
    }
    return $number;
}

[download]

produces

                   1
                  12
                ,123
               1,234
              12,345
             123,456
           1,234,567
          12,345,678
         123,456,789
        1234,567,890
      12,345,678,901
     123,456,789,012
    1234,567,890,123
   12345,678,901,234

[download]

As you can see, it breaks out of the while too soon as it has not kept up with the increasing length of the number as the commas go in. I agree that it would be nice to factor abs and length out of the loop but can't quite see how to achieve it.

Cheers,

JohnGG

In reply to Re^3: Formatting a number by johngg
in thread Formatting a number by harryf

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