Fordítóprogramok 4. gyak

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


namespace vegesdetautomata
{
    class FileHandler
    {
        private string _szoveg { get; set; }
        public void Open(string fileName)
        {

            using (FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read))
            {
                using (StreamReader s = new StreamReader(fs))
                {
                    while (!s.EndOfStream)
                    {
                        _szoveg = s.ReadToEnd();
                        Console.WriteLine(_szoveg);
                    }
                }
            }
        }

        public string Read(string filename)
        {
            Open(filename);
            return _szoveg;
        }

        public string[] ReadAndSplit(string filename)
        {
            return Read(filename).Split(new char[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries);
        }

        public void Save(string fileName)
        {
            using (StreamWriter writer = new StreamWriter(fileName, true))
            {
                writer.Write(_szoveg);
                writer.Flush();
            }

        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            List<string> validStrings = new List<string>();
            foreach (var str in new FileHandler().ReadAndSplit("proba.txt"))
            {
                string A = "q0";
                for (int i = 0; i < str.Length && A != "error"; i++)
                {
                    A = Delta(A, str[i]);
                }
                if (A != "error" && A != "q0") validStrings.Add(str);
            }

            Console.WriteLine("\n\n--------------\nValid strings:");
            foreach (var str in validStrings)
            {
                Console.WriteLine(str);
            }
            Console.ReadLine();

        }

        static string Delta(string allapot, char s)
        {

            switch (allapot + GetAllapot(s))
            {
                case "q0-": return "q1";
                case "q0+": return "q1";
                case "q0N": return "q2";
                case "q1N": return "q2";
                case "q2N": return "q2";
            }
            return "error";
        }

        static string GetAllapot(char str)
        {
            if (Char.IsDigit(str)) return "N";
            else if (str.ToString() == "-") return str.ToString();
            return "nö1q345göeqa83754zz"; // because fuck you, that's why
        }
    }
}