help adding text from richtextbox 1 with richtextbox2 C#

Question

Hello, I would like to know how I do, so when I type in richtextbox1 the text appears in richtextbox2, exactly as if it were a line counter, each time you press enter, only with a number of its own, type a1, A9, b, C4, C5......
see in the image here

Answer 1

The numbering you say has a logical sequence?

I suggest, put an event in the keypress of your richtextbox1

I transferred the text of rchtb1 to an array (Split breaking the lines at each Enter) for each line I wrote on rchtb2 and broke the line.

private void richTextBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (e.KeyChar == 13)
    {
        richTextBox2.Clear();
        string texto = richTextBox1.Text;
        string[] linhas = texto.Split('\n');
        foreach (string linha in linhas)
        {
            richTextBox2.AppendText(linha + Environment.NewLine);
        }
    }
}

If you want to define this sequence, which I did not understand very well, you should put before the variable linha in the richTextBox2.AppendText.