Barcode Generator

#include <iostream>

using namespace std;

int main() {
    int startNum, finalNum;
    cin >> startNum >> finalNum;

    for (int a = startNum / 1000; a <= finalNum / 1000; a++) {
        for (int b = startNum / 100 % 10; b <= finalNum / 100 % 10; b++) {
            for (int c = startNum / 10 % 10; c <= finalNum / 10 % 10; c++) {
                for (int d = startNum % 10; d <= finalNum % 10; d++) {
                    if (a % 2 == 1 && b % 2 == 1 && c % 2 == 1 && d % 2 == 1) {
                        cout << a << b << c << d << " ";
                    }
                }
            }
        }
    }
    return 0;
}

ИЛИ:

#include <iostream>

using namespace std;

int main() {
    string startNum, finalNum;
    cin >> startNum >> finalNum;

    for (int a = startNum[0]; a <= finalNum[0]; a++) {
        for (int b = startNum[1]; b <= finalNum[1]; b++) {
            for (int c = startNum[2]; c <= finalNum[2]; c++) {
                for (int d = startNum[3]; d <= finalNum[3]; d++) {
                    if (a % 2 == 1 && b % 2 == 1 && c % 2 == 1 && d % 2 == 1) {
                        cout << char(a) << char(b) << char(c) << char(d) << " ";
                    }
                }
            }
        }
    }
    return 0;
}