PAT 1035. Password

#include <cstdio>
#include <cstdlib>
#include <vector>

using namespace std;

class Item {
public:
    char uid[12];
    char pwd[12];
};

char tbl[256];

void init_tbl() {
    for (int i=0; i<256; i++) {
        tbl[i] = i;
    }
    tbl['1'] = '@';
    tbl['0'] = '%';
    tbl['l'] = 'L';
    tbl['O'] = 'o';
}

int main() {
    int N;
    scanf("%d", &N);
    vector<Item> ids(N);
    vector<int> changed;
    
    init_tbl();
    
    int len = ids.size();
    for (int i=0; i<len; i++) {
        scanf("%s%s", ids[i].uid, ids[i].pwd);
        bool updated = false;
        int k = 0;
        char ch = '