Summary	BookNumber deals with the ISBN, International Symbolic Book Number, which involves error detection. It uses a deceptively simple algorithm, which can be done in many ways.
Topics	It involves four different representations of a book Number (integer, string, array, tree) and various ways of "parsing" such types.
Audience	It can be introduced at a very early stage in CS0 and reoccurs at other stages in CS1, including simple trees in CS2.
Difficulty	It begins very easily, but advances to medium (when done with trees)
Strengths	It emphasizes the concept of MANY; the fact that many data types can represent an ISBN, and MANY algorithms can compute the ISBN checkSymbol.
Weaknesses	Students may get bored with the same simple example, used repeatedly.
Dependencies	This project does not depend on any one form
Variants	This standard 10 digit code is being extended to 13 digits by 2007. Many bar code systems are similar in nature to the ISBN structure