SWEA 3750 - Digit sum

문제 링크 : https://www.swexpertacademy.com/main/code/problem/problemDetail.do?contestProbId=AWHPiSYKAD0DFAUn

문제의 저작권은 SW Expert Academy에 있습니다.

#include <cstdio>
 
using namespace std;
 
unsigned long int f(unsigned long int n) {
    if(n < 10)
        return n;
    else {
        unsigned long int temp = 0;
        while(n > 9) {
            temp += n%10;
            n = n/10;
        }
        return f(temp + n);
    }
}
 
int main(void) {
    int T;
    unsigned long int n;
    scanf("%d", &T);
 
    for(int t_case=1; t_case<=T; t_case++) {
        scanf("%ld", &n);
        printf("#%d %d\n", t_case, f(n));
    }
 
    return 0;
}