C programming question Given n, take the sum of the digits of n. If that value has more than one digit, continue reducing in this way until a single-digit number is produced. The input will be a non-negative integer.

int digitSum(int n) {

int sum = 0;

while (n) {

 sum += n % 10;

 n /= 10;

}  

return sum < 10 ? sum : digitSum(sum);

}

int main()

{

int n = 12345;

printf("Digit sum of %d is %d\n", n, digitSum(n));

}

Explanation:

The recursion takes care of the repeated summing in case the sum has more than 1 digit.