Dutch bank-account numbers must pass the "elf-proef" (eleven-test) to be valid. This sub tests if a number is a valid account number.
sub elfProef ($) {
        my ($account) = @_;
        die("elfproef: `$account' isn't 9 characters long\n")
                unless length($account) == 9;

        my $sum = 0;
        foreach (reverse(-9..-1)) {
                $sum += (substr($account, $_, 1) * abs($_));
        }

        return not ($sum % 11);
}

[download]

Replies are listed 'Best First'.
Re: Elfproef (Dutch bank account check)
by CheeseLord (Deacon) on Jul 28, 2001 at 22:40 UTC

    This might just be a matter of taste, but I wouldn't die if the string wasn't 9 digits long; instead, I'd return false, as it clearly is an invalid number. I'm a bit wary of having subroutines cause my program to die. Then again, I don't know the context of the sub in your program. :-)

    Also, if you're going to check the input for validity, you might also test that the string contains all digits; /^\d{9}$/ would take care of both conditions. Just some things to think about.

    His Royal Cheeziness

[reply]
[d/l]
Re: Elfproef (Dutch bank account check)
by petral (Curate) on Jul 27, 2001 at 01:52 UTC
    Not that it matters unless I'm missing something, but why not:
            foreach (1..9)) {
                $sum += (substr($account, $_-1, 1) * $_);
        }

    [download]
    ?

      p

[reply]
[d/l]
      Because you have to multiply the last number by 1, the second to last by 2, etc. 
       $sum += (substr($account, $_-1, 1) * $_);

      [download]
      multiplies the first by 1, the second by 2 (the wrong way around :)
[reply]
[d/l]
        Oh, right.  I guess the only simplification would be
        $sum += substr($account, -$_, 1) * $_;

        [download]
        Anyway, good code.

          p

[reply]
[d/l]

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