##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
(Loop until single digit)
Keep summing digits until num < 10. To extract digits, use num % 10 for the last digit and num / 10 to remove it.
Pseudocode: while num >= 10: sum = 0; while num > 0: sum += num % 10; num /= 10; num = sum. Return num.
This works but is slow. There is a faster way using modular arithmetic.
