I solved it after looking up StackOverflow for examples around the modulus or remainder (%). I copied code, changed it to mine, and solved the puzzle, but now I still don't how this works EXACTLY. int sum = 0; while (number > 0) { sum = sum + number % 10; number = number / 10; } return sum; Can someone in plain English explain what this code does, step by step? It seems rather important, so I actually want to understand what I'm doing, instead of just copying stuff of the internet.