EGN

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

namespace ValidatonNumberCopy1
{
    class Program
    {
        public static int RemainingDaysToBirthday(DateTime birthday)
        {
            var nextBirthday = birthday.AddYears(DateTime.Today.Year - birthday.Year);
            if (nextBirthday < DateTime.Today)
            {
                nextBirthday = nextBirthday.AddYears(1);
            }
            return (nextBirthday - DateTime.Today).Days;
        }
        static void Main(string[] args)
        {
            try
            {

                bool correctCount = true;
                bool correctMonth = true;
                bool correctSixthSeventh = true;
                bool correctValidationNumber = true;
                bool correctDayOfBirth = true;
                string monthStr = "";
                int month = 0;
                string yearLastDigitsStr = "";
                int yearLastDigits = 0;
                string dateOfBirthStr = "";
                int dayOfBirth = 0;
                long[] arrayDigits = new long[0];
                do
                {
                    Console.Write("Enter EGN: ");
                    string EGNStr = Console.ReadLine();
                    //string EGNStr = "9203127630";
                    int digitsCount = EGNStr.Length;

                    // Check for exactly 10 digits
                    correctCount = true;
                    if (digitsCount != 10)
                    {
                        correctCount = false;
                        continue;
                    }

                    long EGN = long.Parse(EGNStr);
                    arrayDigits = new long[digitsCount];
                    for (int i = 0; i < arrayDigits.Length; i++)
                    {
                        arrayDigits[(arrayDigits.Length - 1) - i] = EGN % 10;
                        EGN = EGN / 10;
                    }


                    // Check for correct month
                    monthStr = EGNStr.Substring(2, 2);
                    month = int.Parse(monthStr);
                    correctMonth = ((month > 0 && month < 13) || (month > 20 && month < 33) || (month > 40 && month < 53));
                    if (!correctMonth)
                    {
                        correctMonth = false;
                        continue;
                    }

                    // Check for correct date of birth
                    dateOfBirthStr = EGNStr.Substring(4, 2);
                    dayOfBirth = int.Parse(dateOfBirthStr);
                    if (!(dayOfBirth > 0 && dayOfBirth < 32))
                    {
                        correctDayOfBirth = false;
                        continue;
                    }

                    // Check for sixth and seventh digit
                    string sixthAndSeventhDigitStr = EGNStr.Substring(6, 2);
                    int sixthAndSeventhDigit = int.Parse(sixthAndSeventhDigitStr);
                    correctSixthSeventh = true;
                    if (!(sixthAndSeventhDigit != 0 && sixthAndSeventhDigit != 88))
                    {
                        correctSixthSeventh = false;
                        continue;
                    }

                    // Check validation number
                    int[] validationDigits = { 2, 4, 8, 5, 10, 9, 7, 3, 6 };
                    long validationSum = 0;
                    for (int i = 0; i < validationDigits.Length; i++)
                    {
                        validationSum = validationSum + (arrayDigits[i] * validationDigits[i]);
                    }
                    long validationNumber;
                    long residue = validationSum / 11;
                    if (residue > 10)
                    {
                        validationNumber = 0;
                    }
                    else
                    {
                        validationNumber = validationSum / 11;
                    }
                    correctValidationNumber = (validationNumber == arrayDigits[9]);
                    yearLastDigitsStr = EGNStr.Substring(0, 2);
                    yearLastDigits = int.Parse(yearLastDigitsStr);
                } while (!(correctCount && correctMonth && correctSixthSeventh && correctValidationNumber && correctDayOfBirth));

                Console.WriteLine("Personal information: ");
                Console.Write("- Gender: ");
                string gender = "";
                if (arrayDigits[8] % 2 == 0)
                {
                    gender = "male";
                }
                else
                {
                    gender = "female";
                }
                Console.WriteLine(gender);

                int yearOfBirth = 0;
                if (month > 0 && month < 13)
                {
                    yearOfBirth = 1900 + yearLastDigits;
                }
                else if (month > 20 && month < 33)
                {
                    yearOfBirth = 1800 + yearLastDigits;
                    month = month - 20;
                }
                else
                {
                    yearOfBirth = 2000 + yearLastDigits;
                    month = month - 40;
                }
                DateTime date = DateTime.Now;
                int currentYear = date.Year;
                int age = currentYear - yearOfBirth;
                Console.Write("- Age: ");
                Console.WriteLine(age);

                Console.Write("- Date of birth: ");
                DateTime birthday = new DateTime(yearOfBirth, month, dayOfBirth);
                string format = "dd MMMMMMMMMM yyyy";
                Console.WriteLine(birthday.Date.ToString(format));

                Console.Write("- Days remaining to the next birthday: ");
                int remainingDays = RemainingDaysToBirthday(birthday);
                Console.WriteLine(remainingDays);
            }
            catch (FormatException)
            {
                Console.WriteLine("You have entered a number containing some characters.");
            }


        }
    }
}