有点迷

第4和8有问题，， 第4个例子我输出的是Right,答案也是Right,,居然是WA？？？

#include<bits/stdc++.h>
using namespace std;
#define ll long long

int main() {
    string str;
    getline(cin, str);
    int a[10];
    a[1] = str[0];
    a[2] = str[2];
    a[3] = str[3];
    a[4] = str[4];
    a[5] = str[6];
    a[6] = str[7];
    a[7] = str[8];
    a[8] = str[9];
    a[9] = str[10];
    int res = 0;
    for (int i = 1; i <= 9; ++i) {
        res += i * (a[i] - '0');
        res %= 11;
    }
    int n = str.size() - 1;
    if (res == 10) {
        if (str[n] == 'X')cout << "Right" << endl;
        else {
            str[n] = 'X'; cout << str << endl;
        }
    }
    else if(res == str[n]-'0')cout << "Right" << endl;
    else {
        str[n] = res + '0';
        cout << str << endl;
    }
    return 0;
}