Read a single non-negative integer n and print the sum of its decimal digits, in the form Digit sum: 16.
You’re not allowed to treat the number as a string here – pull digits off the end of the number using % 10
(remainder when dividing by 10 gives the last digit) and / 10 (integer division drops that digit), repeating
until nothing is left. This pattern – peel off the low digit, shrink the number, repeat – shows up constantly:
reversing a number, converting bases, checking for palindromes. Trace n = 493 by hand before you code it: what are
n, n % 10, and n / 10 after each iteration?