How to double the file size?

Question

C++ / C#

Help me write a file with the same bits, only to have 2 times more of them, otherwise I have already broken my head. Below is a bit by bit reading.

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

namespace hdlc_ip
{
    class Program
    {
        static void Main(string[] args)
        {
            FileStream file = new FileStream("C:\\2.txt",
                FileMode.Open, FileAccess.Read);
            byte[] buf = new byte[1024];
            File.Copy("C:\\2.txt", "3.txt",true);
            int r = -1;
            byte b;
            //StreamWriter print = new StreamWriter("C:\\2.txt", true);
            //string read = File.ReadAllText("C:\\2.txt");
            //print.Write(read);
            while (r != 0)
            {
                r = file.Read(buf, 0, buf.Length);
                for (int j = 0; j < r; j++)
                {
                    b = buf[j];
                    for (int i = 7; i >= 0; i--)
                        
                        Console.Write((b >> i) & 1);
                    Console.Write((j + 1) % 4 == 0 ? '\n' : ' ');
                }
            }
            file.Close();
      
            Console.ReadKey(true);
        }
    }
 
}

Answer 1

If you stupidly double the file, then like this:

class Program
    {
        static void Main(string[] args)
        {
            string filename = "C:\\1.txt";
            byte[] filebytes = File.ReadAllBytes(filename);
            using (FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Write, FileShare.None))
            {
                fs.Seek(0, SeekOrigin.End);
                fs.Write(filebytes, 0, filebytes.Length);
            } // using fs
        } // Main
    } // class Program