# NAME

CheckDigits::MXX_002 - compute check digits for CAS

# SYNOPSIS

``````  use Algorithm::CheckDigits;

\$cas = CheckDigits('cas');

if (\$cas->is_valid('1333-74-0')) {
# do something
}

\$cn = \$cas->complete('1333-74-');
# \$cn = '1333-74-0'

\$cd = \$cas->checkdigit('1333-74-0');
# \$cd = '0'

\$bn = \$cas->basenumber('1333-74-0');
# \$bn = '1333-74-'
``````

# DESCRIPTION

## ALGORITHM

1. Beginning right with the second digit all digits are weighted ascending starting with 1.

2. The sum of those products is computed.

3. The checksum is the last digit of the sum from step 2 (modulo 10).

## METHODS

is_valid(\$number)

Returns true only if `\$number` consists solely of numbers and the last digit is a valid check digit according to the algorithm given above.

Returns false otherwise,

complete(\$number)

The check digit for `\$number` is computed and concatenated to the end of `\$number`.

Returns the complete number with check digit or '' if `\$number` does not consist solely of digits and spaces.

basenumber(\$number)

Returns the basenumber of `\$number` if `\$number` has a valid check digit.

Return '' otherwise.

checkdigit(\$number)

Returns the checkdigit of `\$number` if `\$number` has a valid check digit.

Return '' otherwise.

None by default.

# AUTHOR

Mathias Weidner, `<mamawe@cpan.org>`

# THANKS

Aaron W. West pointed me to a fault in the computing of the check digit.

HERMIER Christophe made me aware that CAS is now assigning 10-digit CAS Registry Numbers (http://www.cas.org/newsevents/10digitrn.html)