Task

Validate the check digit of an ISBN-13 code:

   Multiply every other digit by  3.
   Add these numbers and the other digits.
   Take the remainder of this number after division by  10.
   If it is  0,   the ISBN-13 check digit is correct.


Use the following codes for testing:

   978-1734314502       (good)
   978-1734314509         (bad)
   978-1788399081       (good)
   978-1788399083         (bad)


Show output here, on this page



See also

   for details:   13-digit ISBN method of validation.       (installs cookies.)


def validISBN13?(str)
  cleaned = str.delete("^0-9").chars
  return false unless cleaned.size == 13
  cleaned.each_slice(2).sum{|d1, d2| d1.to_i + 3*d2.to_i }.remainder(10) == 0
end
 
isbns = ["978-1734314502", "978-1734314509", "978-1788399081", "978-1788399083"]
isbns.each{|isbn| puts "#{isbn}: #{validISBN13?(isbn)}" }
 