题解 | #Digital Roots# #C

#include <stdio.h>

int main() {
    int a;
    while (scanf("%d", &a) != EOF) {
        int sum=0;
        while (1) {
            sum=0;
            while (a) {
                sum+=a%10;
                a/=10;
            }
            if (sum<10){
                break;
            }else {
                a=sum;
            }
        }
        printf("%d\n", sum);
    }
    return 0;
}