杭电1013超时

#include<iostream>
using namespace std;

int f(int n)
{
    int sum = 0;
    while(n)
    {
        sum += n%10;
        if(sum > 9)
            sum = sum %10 + sum/10;
        n /= 10;
    }
    return sum;
}
int main()
{
    int n;
    while(cin >> n, n != 0)
    {
        cout << f(n) << endl;
    }
    return 0;
}

应该是数位开的太小，导致死循环了，改进如下：

#include<iostream>
#include<string>
using namespace std;

int f(string s)
{
    int sum = 0;
    for(int i = 0; i < s.size(); ++i)
    {
        sum += s[i] - '0';
        if(sum > 9)
            sum = sum %10 + sum/10;
    }
    return sum;
}
int main()
{
    string s;
    while(cin >> s, s != "0")
    {
        cout << f(s) << endl;
    }
    return 0;
}