求改

#include <bits/stdc++.h>
using namespace std;
int V = 1e6 + 10;
int main()
{
    string a;
    cin >> a;
    int z[V];
    for (int i = 0 ; i<= a.size(); i++)
    {
     if (a[i] >= '0' && a[i] <= '9')
         z[++i] = a[i] - '0';
    }
    sort(a+1 , a+k+1);
    for (int u = 1; u <= k;u++)
        cout << z[u];
    return 0;
}