Recursion: sum digits of a number until there is a single digit left

Question

How can I sum digits of a number in a recursive manner until there is only a single digit left?

Example: with the input 9234, the result would be 9 because 9 + 2 + 3 + 4 = 18 and then 1 + 8 = 9.

This is my code for the moment but I want to sum until there is only a single digit

int getsum(int n) {
   return n == 0 ? 0 : n % 10 + getsum(n/10);
}

Answer 1

There are several possibilities, here is one of them:

public static int getSum(int n) {
     int s = getSumHelper(n); // your original (private) method
     while (s > 9)
         s = getSumHelper(s);
     return s;
}

EDIT: Your original code for completeness, because there seems to be confusion.

private static int getSumHelper(int n) {
    return n == 0 ? 0 : n % 10 + getSumHelper(n/10);
}