Divide by three without using numeric operators...

gistfile1.pl

use strict;
use warnings;
no warnings 'numeric';

print "$_ -> " . div3( $_ ) . "\n" for map { $_ / 10 } 0 .. 10;
print "$_ -> " . div3( $_ ) . "\n" for 0 .. 10;


sub div3 {
    my $input = shift;

    # Turn it in to its digits, casting in to a string
    my @digits = split //, $input;

    # Create a 30-item list. This should be done outside the loop, obv
    my @lookup = map { [$_,0], [$_,1], [$_,2] } 0 .. 9;

    # You could do this more gracefully with reduce, but it's easier to
    # understand this way. This is the 'digit' we carry
    my $carry = '';

    # We'll build up a string output here
    my $output = '';

    # Have we passed a decmial?
    my $float = 0;

    # For every digit...
    while ( @digits ) {
        my $digit = shift( @digits );

        # Pass the period through, noting that we're now in floating territory
        if ( $digit eq '.' ) {
            $float = 1;
            $output .= '.';

        # Otherwise
        } else {

            # Concatenate the carry 'digit' and the current 'digit'
            $digit = $carry . $digit;

            # Lookup how that divides by three
            my ( $result, $remainder ) = @{ $lookup[ $digit ] };

            # If the remainder is 0, we actually want a zero-length string
            $carry = $remainder || '';

            # Unless it's a leading 0, add the number to our output
            $output .= $result if length( $output ) || $result;

            # If we have a carry but are all out of digits, round
            if ( $carry && ! @digits ) {
                unless ( $float ) { $output .= '.' }
                $output .= [1,4,7]->[$carry];
                last;
            }
        }
    }

    return $output || 0;
}