Isbn Verifier in C#
Check if a given string is a valid ISBN-10 number.
exercism fetch csharp isbn-verifier
Check if a given ISBN-10 is valid.
Given an unknown string the program should check if the provided string is a valid ISBN-10. Putting this into place requires some thinking about preprocessing/parsing of the string prior to calculating the check digit for the ISBN.
The program should allow for ISBN-10 without the separating dashes to be verified as well.
Let's take a random ISBN-10 number, say
3-598-21508-8 for this.
The first digit block indicates the group where the ISBN belongs. Groups can consist of shared languages, geographic regions or countries. The leading '3' signals this ISBN is from a german speaking country.
The following number block is to identify the publisher. Since this is a three digit publisher number there is a 5 digit title number for this book.
The last digit in the ISBN is the check digit which is used to detect read errors.
The first 9 digits in the ISBN have to be between 0 and 9. The check digit can additionally be an 'X' to allow 10 to be a valid check digit as well.
A valid ISBN-10 is calculated with this formula
(x1 * 10 + x2 * 9 + x3 * 8 + x4 * 7 + x5 * 6 + x6 * 5 + x7 * 4 + x8 * 3 + x9 * 2 + x10 * 1) mod 11 == 0
So for our example ISBN this means:
(3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 1 * 5 + 5 * 4 + 0 * 3 + 8 * 2 + 8 * 1) mod 11 = 0
Which proves that the ISBN is valid.
Note that, when trying to submit an exercise, make sure the exercise file that you're submitting is in the
For example, if you're submitting
bob.cs for the Bob exercise, the submit command would be something like
exercism submit <path_to_exercism_dir>/csharp/bob/bob.cs.
Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.