求大佬debug

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

int main()
{
    char ch;
    string a;
    cin >> a;
    int c[10], i = 0, sum = 0;
    for (auto b : a)
    {
        if (isdigit(b))
        {
            c[i] = b;
            i++;
        }
    }
    for (int x = 0; x < 9; x++)
    {
        sum = sum + c[x] * (x + 1);
    }
    sum %= 11;
    if (sum == c[10])
    {
        cout << "right";
    }
    else if (sum == 10)
    {
        ch = 'X';
        a.pop_back();
        a.push_back(ch);
    }
    else
    {
        a.pop_back();
        ch = sum + '0';
        a.push_back(ch);
        cout << a;
    }

    return 0;
}