Sum of Digits of a Number until Sum becomes Single Digit

Problem Statement:

Program to find sum of digits of a given number until sum becomes single digit.

Source Code:

#include<stdio.h>
int main(){
    int num,sumOfDigits=0;
    scanf("%d",&num);
    while(num!=0){
        sumOfDigits += num%10;
        num /= 10;
        if(num==0 && sumOfDigits>9){
            num = sumOfDigits;
            sumOfDigits = 0;
        }
    }
    printf("%d",sumOfDigits);
    return 0;
}

SAMPLE INPUT:
555
SAMPLE OUTPUT:
6