using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.IO;

public class Program

{

    public static void Main ()

    {

        StreamReader sr = new StreamReader("Plik.exe");

        while (!sr.EndOfStream)

        {

            string s = sr.ReadLine();

            Console.WriteLine(s);

        }

        sr.Close();

        StreamWriter sw = new StreamWriter("Plik.exe", true);

        sw.WriteLine(Console.ReadLine());

        sw.Close();

        string all = sr.ReadToEnd();

    }   

}

​