为啥用getline不行

#include <bits/stdc++.h>

using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    freopen("test.in", "r", stdin);
    freopen("test.out", "w", stdout);
    string str;
    while (cin>>str)
    {
        int sum = 0, start = 0;
        for (int i = 1; i <= 9; i++)
        {
            if (str[start] == '-')
                start++;
            sum += i * (str[start] - '0');
            start++;
        }
        sum %= 11;
        if (sum == 10)
            sum = 'X';
        else
            sum += '0';
        if (sum == str[str.length() - 1])
            cout << "Right" << endl;
        else
        {
            str[str.length() - 1] = sum;
            cout << str << endl;
        }
    }
}

为啥输入的时候用cin可以AC，用getline就不行？