This is the code I've seen so far to delete last 3 lines in a text file, but it's required to determine string[] lines = File.ReadAllLines(); which is nt necessary for me to do so.

string[] lines = File.ReadAllLines(@"C:\\Users.txt");
            StringBuilder sb = new StringBuilder();
            int count = lines.Length - 3; // except last 3 lines 
            for (int s = 0; s < count; s++)
            {
                sb.AppendLine(lines[s]);

            }

The code works well, but I don't wanna re-read the file as I've mentioned the streamreader above :

using (StreamReader r = new StreamReader(@"C:\\Users.txt"))

Im new to C#, as far as I know, after using streamreader, and if I wanna modify the lines, I have to use this :

while ((line = r.ReadLine()) != null)
{
#sample codes inside the bracket
                    line = line.Replace("|", "");
                    line = line.Replace("MY30", "");
                    line = line.Replace("E", "");
}

So, is there any way to delete the last 3 lines in the file within the "while ((line = r.ReadLine()) != null)" ??

I have to delete lines, replace lines and a few more modications in one shot, so I can't keep opening/reading the same text file again and again to modify the lines. I hope the way I ask is understable for you guys >.<

Plz help me, I know the question sounds simple but I've searched so many ways to solve it but failed =(

So far, my code is :

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

namespace ConsoleApplication11
{
public class Read
{

    static void Main(string[] args)
    {

        string tempFile = Path.GetTempFileName();
        using (StreamReader r = new StreamReader(@"C:\\Users\SAP Report.txt"))
        {
            using (StreamWriter sw = new StreamWrite (@"C:\\Users\output2.txt"))
            {
                string line;

                while ((line = r.ReadLine()) != null)
                {
                    line = line.Replace("|", "");
                    line = line.Replace("MY30", "");
                    line = line.Replace("E", "");

                    line = System.Text.RegularExpressions.Regex.Replace(line, @"\s{2,}", " ");

                    sw.WriteLine(line);
                }
     }
            }
        }
    }
}

Now my next task is to delete the last 3 lines in the file after these codes, and I need help on this one.

Thank you.