Sum of Digits - Problem Statement

Given a positive integer $n$, find the sum of its digits. For example, if $n = 1234$, the answer is $1 + 2 + 3 + 4 = 10$. You will use recursion.

The key point: you can split $n$ into its last digit ($n \bmod 10$) and the remaining digits ($\lfloor n / 10 \rfloor$). Then the sum is last digit plus the sum of the rest. This gives you a natural recursive structure. Before reading the solution, try to identify the base case yourself. When is the answer obvious without recursion?