Append text at a certain row in a txt-file

Hi.

I'm trying to append text to a txt file at a certain row.
For example:
a
b
c
d

And after I run the program and append 'z' at row 3, it should look like:
a
b
cz
d

Does anyone know how to do this? I can't seem to get append to work, only overwriting.

Code:

---

                private void button1_Click(object sender, System.EventArgs e)
                {
                        System.Text.StringBuilder buffer = new System.Text.StringBuilder();
                        System.IO.StreamReader reader = System.IO.File.OpenText("C:\\Temp\\New Text Document.txt");
                        Int32 lineCount = 1;

                        while (reader.Peek() != -1)
                        {
                                if (lineCount == 3)
                                {
                                        buffer.Append(reader.ReadLine());
                                        buffer.Append("z");
                                }
                                else
                                {
                                        buffer.Append(reader.ReadLine());
                                }
                                buffer.Append(Environment.NewLine);
                                lineCount++;
                        }
                        reader.Close();

                        System.IO.StreamWriter writer = new System.IO.StreamWriter("C:\\Temp\\New Text Document.txt",false);
                        writer.Write(buffer.ToString());
                        writer.Flush();
                        writer.Close();
        }

---

Works great!
Thanks a lot!

these codes works
private void button1_Click(object sender, System.EventArgs e)
{
System.Text.StringBuilder buffer = new System.Text.StringBuilder();
System.IO.StreamReader reader = System.IO.File.OpenText("C:\\Temp\\New Text Document.txt");
Int32 lineCount = 1;

while (reader.Peek() != -1)
{
if (lineCount == 3)
{
buffer.Append(reader.ReadLine());
buffer.Append("z");
}
else
{
buffer.Append(reader.ReadLine());
}
buffer.Append(Environment.NewLine);
lineCount++;
}
reader.Close();

System.IO.StreamWriter writer = new System.IO.StreamWriter("C:\\Temp\\New Text Document.txt",false);
writer.Write(buffer.ToString());
writer.Flush();
writer.Close();
}

but how if i would like these output?
a b c d
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4

tnx

Code:

---

private void button1_Click(object sender, System.EventArgs e)
{

        string myPath = "C:\\New Text Document.txt";
        if (! System.IO.File.Exists(myPath))
        {
                WriteData(string.Empty,myPath);
        }

        System.Text.StringBuilder buffer = new System.Text.StringBuilder();
        System.IO.StreamReader reader = System.IO.File.OpenText(myPath);
        bool firstLine = true;

    while (reader.Peek() != -1)
        {
                string currentLine = reader.ReadLine();
                                        char lastChar = Convert.ToChar(currentLine.Substring(currentLine.Length - 1));
               
                if (firstLine)
                {
                        lastChar = (char)(lastChar + 1);
                        firstLine = false;
                }

                buffer.Append(currentLine);
                buffer.Append(" ");
                buffer.Append(lastChar);
                buffer.Append(Environment.NewLine);
        }
        reader.Close();

        //handle the first write
        if (firstLine)
        {
                buffer.Append("a");
                buffer.Append(Environment.NewLine);
                for (int i = 1; i <= 4; i++)
                {
                        buffer.Append(i.ToString());
                        buffer.Append(Environment.NewLine);
                }
        }
        WriteData(buffer.ToString().TrimEnd(),myPath);
}

private void WriteData(string data,string path)
{
        System.IO.StreamWriter writer = new System.IO.StreamWriter(path,false);
        writer.Write(data);
        writer.Flush();
        writer.Close();
}

---

FileStream stmRecords = new FileStream(@"C:\Scanned.txt", FileMode.Append, FileAccess.Write, FileShare.None);
StreamWriter stmWriter = new StreamWriter(stmRecords);

stmWriter.WriteLine(var1 + " , " + var2);

stmWriter.Flush();
stmWriter.Close();


tnx for ur reply but this is what i searched. it's kinda easy to understand.
except the stmWriter.Flush(); i don't jknow its function.
but if someone has the same problem above code will do.