Paswort generator

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

namespace ConsoleApplication56
{
    class Program
    {
        static void Main(string[] args)
        {

            int eingabe = 0, eingabe2 = 0;
            bool success = true;
            bool success1 = true;
            string  passwort1;






            string[] Textdatei = new string[100];


            Console.WriteLine("Wollen Sie sich registrieren[1] oder anmelden[2]?");



            while (success == true)
            {
                try
                {
                    eingabe = Convert.ToInt16(Console.ReadLine());
                    success = false;
                }
                catch (System.FormatException)
                {
                    Console.WriteLine("Fehler bitte erneut eingeben!");
                }
            }

            if (eingabe == 1)
            {
                Console.WriteLine("Wollen Sie ihr eigenes Passwort[1] nehmen oder unseres[2]");


                while (success1 == true)
                {
                    try
                    {
                        eingabe2 = Convert.ToInt16(Console.ReadLine());
                        success1 = false;
                    }
                    catch (System.FormatException)
                    {
                        Console.WriteLine("Fehler! Bitte erneut eingeben");
                    }

                }





                if (eingabe2 == 1)
                {
                    Console.WriteLine("Geben Sie bitte ihren neuen Benutzernamen und Passwort ein");

                    using (StreamWriter writer = new StreamWriter("Benutzernamen.txt", true))
                    {


                        writer.WriteLine(Console.ReadLine());


                    }

                    using (StreamWriter writer = new StreamWriter("Passwörter.txt", true))
                    {


                        writer.WriteLine(Console.ReadLine());


                    }







                }

                if (eingabe2 == 2)
                {

                    Console.WriteLine("Geben Sie bitte ihr dazugehörigen Benutzernamen ein");



                    using (StreamWriter writer = new StreamWriter("Benutzernamen.txt", true))
                    {


                        writer.WriteLine(Console.ReadLine());


                    }


                    Console.Write("Länge des Passworts: ");
                    int length = int.Parse(Console.ReadLine());
                    Console.Write("Großbuchstaben verwenden (j/n): ");
                    bool upperCase = Console.ReadLine() == "j";
                    Console.Write("Kleinbuchstaben verwenden (j/n): ");
                    bool lowerCase = Console.ReadLine() == "j";
                    Console.Write("Ziffern verwenden (j/n): ");
                    bool digits = Console.ReadLine() == "j";
                    Console.Write("Sonderzeichen verwenden (j/n): ");
                    bool specialChars = Console.ReadLine() == "j";


                    passwort1 = createPassword(lowerCase, upperCase, digits, specialChars, length);
                    Console.WriteLine("Ihr generiertes Passwort:" + passwort1);

                    System.IO.StreamWriter kek =
                           new System.IO.StreamWriter("Passwörter.txt");

                    using (StreamWriter writer = new StreamWriter("Benutzernamen.txt", true))
                    {


                        writer.WriteLine(Console.ReadLine());
                        writer.WriteLine(passwort1);


                    }




                }



            }



            if (eingabe == 2)
            {

                Console.Write("Bitte geben Sie hier ihren Benutzernamen an: ");
                string strUsername = Console.ReadLine();
                string strTUsername = "testuser";
                if (strUsername == strTUsername)
                {
                    Console.Write("Bitte geben Sie hier ihr Passwort an: ");
                    Console.ForegroundColor = ConsoleColor.Black;
                    string strPassword = Console.ReadLine();
                    string strTPassword = "testpasswort";
                    if (strPassword == strTPassword)
                    {
                        Console.ForegroundColor = ConsoleColor.Gray;
                        Console.WriteLine("Du bist eingelogged!");



                        string[] Array1 = new string[100];
                        string[] Array2=new string[100];


                        int counter = 0;
                        string line2;

                        System.IO.StreamReader file2 =
                        new System.IO.StreamReader("Benutzernamen.txt");

                        while ((line2 = file2.ReadLine()) != null)
                        {
                            Array1[counter] = file2.ReadLine();
                            Console.WriteLine(Array1[counter]);
                            counter++;
                        }



                        string line;

                        System.IO.StreamReader file =
                        new System.IO.StreamReader("Passwörter.txt");
                        counter = 0;

                        while ((line = file.ReadLine()) != null)
                        {

                            Array2[counter] = file.ReadLine();
                            Console.WriteLine(Array2[counter]);

                            counter++;
                        }

                        for (int i = 0; i < counter; i++)
                        {
                            Console.WriteLine(Array1[i] + "       " + Array2[i]);
                        }

                    }
                    else
                    {
                        Console.ForegroundColor = ConsoleColor.Gray;
                        Console.WriteLine("Falscher Benutzername!: {0}", strUsername);
                        Console.ReadLine();
                    }
                }
                else
                {
                    Console.WriteLine("Falsches Passwort!");
                    Console.ReadLine();
                }

            }

        }





        public static string createPassword(bool lowerCase, bool upperCase, bool digits, bool specialChar, int length)
        {
            string alphabet = "";
            if (lowerCase)
                alphabet += "abcdefghijklmnopqrstuvwxyz";
            if (upperCase)
                alphabet += "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            if (digits)
                alphabet += "0123456789";
            if (specialChar)
                alphabet += "^!\"§$%&/()=?²³{[]}\\`´+*~#',.-;:_<>|";
            if (alphabet.Length == 0)
                return "error";
            StringBuilder result = new StringBuilder();
            Random r = new Random();
            while (result.Length < length)
                result.Append(alphabet[r.Next(alphabet.Length)]);
            return result.ToString();
        }

    }
}