using in C#

using System;
using System.IO;

namespace TestFile
{
    class Program
    {
        //The text file's path is stored in 'filename'
        static string filename = @"C:\Users\Nan\source\repos\Example.txt";

        static void Main(string[] args)
        {
            static void ReadFile()
            {
                using (var fs = new FileStream(filename, FileMode.Open, FileAccess.Read))

                {
                    var b1 = fs.ReadByte();
                    var c1 = (char)b1;

                }
            }
        }
    }
}