1013 Digital Roots

#include<iostream>#include<string>using namespace std;int root(int n){int sum = 0;for (int i = n; i > 0; i = i / 10){sum = sum + i % 10;}return sum;}int main(){int n,num;string s;while (cin >> s){if (s[0] == '0'&&s.size()==1)break;num = 0;for (int i = 0; i <= s.size() - 1; ++i)num = num + s[i] - '0';for (; num > 9;)num = root(num);cout << num << endl;}return 0;}