Book code: the last digit

Python Intermediate alien ages teen+ From CS Unplugged

The problem

An ISBN-10 book code has 10 digits. The last one is a check digit. Write a function isbn10_check_digit(first9) that gets the first 9 digits as text and gives back the check digit as text. How: multiply the digits by 10, 9, 8 ... 2 and add them up. The check digit is (11 - total % 11) % 11. If that is 10, give back "X".

You will practice: check digits, loops, remainder (%), text and numbers

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CC BY-SA 4.0

Adapted from a CS Unplugged programming challenge by the University of Canterbury Computer Science Education Research Group, licensed CC BY-SA 4.0.

Original challenge · License: CC BY-SA 4.0

Changes: Rewritten in our own words as a function with tests, hints and steps, in Python and JavaScript, by Open Cosmos. This version is also CC BY-SA 4.0.