BarcodeGenerator

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BarcodeGenerator
{
    class Program
    {
        static void Main(string[] args)
        {
            string firstNumberAsString = Console.ReadLine(); // "3333"
            string secondNumberAsString = Console.ReadLine(); // "3339"

            int firstStart = (int)Char.GetNumericValue(firstNumberAsString[0]); // -> char '3' -> 3
            int firstEnd = (int)Char.GetNumericValue(secondNumberAsString[0]);

            int secondStart = (int)Char.GetNumericValue(firstNumberAsString[1]);
            int secondEnd = (int)Char.GetNumericValue(secondNumberAsString[1]);

            int thirdStart = (int)Char.GetNumericValue(firstNumberAsString[2]);
            int thirdEnd = (int)Char.GetNumericValue(secondNumberAsString[2]);

            int fourthStart = (int)Char.GetNumericValue(firstNumberAsString[3]);
            int fourthEnd = (int)Char.GetNumericValue(secondNumberAsString[3]);

            // 2323
            firstStart = firstStart % 2 == 0 ? firstStart + 1 : firstStart;
            secondStart = secondStart % 2 == 0 ? secondStart + 1 : secondStart;
            thirdStart = thirdStart % 2 == 0 ? thirdStart + 1 : thirdStart;
            fourthStart = fourthStart % 2 == 0 ? fourthStart + 1 : fourthStart;
            for (int firstDigit = firstStart; firstDigit <= firstEnd; firstDigit += 2)
            {
                for (int secondDigit = secondStart; secondDigit <= secondEnd; secondDigit += 2)
                {
                    for (int thirdDigit = thirdStart; thirdDigit <= thirdEnd; thirdDigit += 2)
                    {

                        for (int fourthDigit = fourthStart; fourthDigit <= fourthEnd; fourthDigit += 2)
                        {
                            Console.Write("{0}{1}{2}{3} ", firstDigit, secondDigit, thirdDigit, fourthDigit);
                        }
                    }
                }
            }
        }
    }
}