题解 | #Digital Roots#（利用goto实现）

#include <iostream>
using namespace std;

int cal(int n){
    int root = 0;

    if(n < 9) return n;

    label: while(n > 0){
        root += n % 10;
        n = n / 10;
    }

    if(root > 9){
        n = root;
        root = 0;
        goto label;
    }
    
    return root;
}

int main(){
    int num;
    while(cin >> num){
        cout << cal(num) << endl;
    }
}