C#| Reading and writing with text files.

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

namespace User_name_with_text_stream
{
    class Program
    {
        static void Main(string[] args)
        {
            string FILE_NAME = "user.txt"; // The file name.
            string Username; // A variable that stores the user name.
            string GetAction;
            if (File.Exists(FILE_NAME)) // Check: If the file exists.
            {
                TextReader read = new StreamReader(FILE_NAME);
                Username = read.ReadLine(); // Reading the username from the file.
                read.Close();
                Console.WriteLine("Hello " + Username);
                Console.Write("To change the username, please input 'Change'\nTo delete the data base, input 'Delete' or 'Erase' (Case Insensitive): ");
                GetAction = Console.ReadLine();
                if (GetAction == "Change" || GetAction == "change")
                {
                    File.Delete(FILE_NAME);
                    Console.Clear();
                    Console.Write("Please enter your username: ");
                    Username = Console.ReadLine();
                    TextWriter write = new StreamWriter(FILE_NAME); // Creating the file.
                    write.WriteLine(Username); // Writing to the file.
                    write.Close();
                    Console.Clear();
                    Console.WriteLine("Account succesfully registered.\nYou may restart the program now.\n(Press 'Enter' to restart the program).");
                }
                else if (GetAction == "Delete" || GetAction == "delete" || GetAction == "Erase" || GetAction == "erase")
                {
                    File.Delete(FILE_NAME);
                    Console.WriteLine("Press 'Enter' to continue..");
                }
                Console.ReadKey();
            }

            else // If the file doesn't exist.
            {
                Console.Write("Please enter your username: ");
                Username = Console.ReadLine();
                TextWriter write = new StreamWriter(FILE_NAME); // Creating the file.
                write.WriteLine(Username); // Writing to the file.
                write.Close();
                Console.Clear();
                Console.WriteLine("Account succesfully registered.\nYou may restart the program now.\n(Press 'Enter' to restart the program).");
                Console.ReadKey();
            }

        }
    }
}