goto next line in MultiLine textBox by keyDown event

no issue. thanks, you point out on my fault. it helps me to learn. i go through http://www.expandinghead.net/keycode.html link and find out the keycodes. so i think it may be ascii codes. :)

They are not, and this is actually good. This multi-step processing helps to abstract out localized input processing for different languages and reserve key strokes which are not related to input text at all (Alt, menu, context menu, etc., and more exotic ones, such as Shift-Shift, Alt-Ctrl (where shift-like keys are used to shift and to generate up or down event).
--SA

have you tried this:- TextBox1.Text = "First line\r\nSecond line";

say example if you want to do enter with 0-9 digit then code would be like,
if(e.KeyCode>=48 && e.KeyCode<=57)
{
textBox3.Text += Environment.NewLine;
}

It "does not work" because you probably use wrong event but the code people show you is correct.
--SA

true

Not true!
--SA

OK, let's get serious. I know the answer. First of all, please tell me the exact type of TextBox. "TextBox" is not a type, this is a name for several different type. Which one in your case, exactly?
--SA

OK, now, what is the type of it? Do you know what is .NET type, and the type in programming?
Probably you did not understand my question, read above carefully. You tell me the type; I'll probably write you an answer. I don't want to write answers for all different .NET libraries I know; even one it too much.
--SA

Have you checked the properties of your TextBox are all set correctly for your requirements; especially this one?

I think we have no evidence that this is System.Windows.Forms.TextBox so far, I'm trying to pull it from OP, but -- look above -- I'm not sure he knows what a control's type means. :-)
--SA

There you go again ...
Evidence of what? I merely asked the OP, not you, whether he or she had checked the documentation for the multiline TextBox (which is what the question is about). Your comment is totally superfluous and unnecessary.

What again, sorry? If you decided that you don't need to see even slight criticism, I will probably try to remember it and avoid but, why. I did not consider you as such a kid who would overreact to every single note. Now you start do give me some epithets. Can we avoid non-technical discussions? "Superfluous"...

OK, this time I'll explain.

The thing is: I know exactly how to do what OP wants, but the answer will be different for Forms, WPF or something else. I'm fed up with trying to answer in 2-3 different variants just because OP does not know that there are some more libraries in addition to those she/he uses. Such double/triple answers (in case of trivial matter like here) is a complete waste of time. I tried to insist that we should not accept the question which has such major ambiguity, for everyone's good.

I explain what evidence. There is nothing wrong in your advice, except... this is yet another attempt to answer the question and post the link which may or may not be relevant to the question, just because the question is ambiguous. And the best advice on this matter is essentially different for Forms and WPF in particular, so I'm not just trying to keep to the principle. And by the way, even if there is some certain information which exactly points to some certain library, I don't want to accept indirect evidence. I think we should insist that the questions are "unambiguous enough".

--SA

The thing is: I know exactly how to do what OP wants
Fine, then leave an answer explaining it. If you had, again, bothered to read my post properly you would see that I merely posed a question for the OP to consider. You then jumped in to say that is not what the OP is asking. How do you know, since he/she has not commented on it? Do you see why I say that your comment is unnecessary and superfluous?

Yes, I do, but in different variants... Your question is your post is correct but the link may or may not be relevant -- this is essentially all.
--SA

Exactly, the link may or may not be relevant, but it is up to the OP to make that determination.

I still wish I could give a really useful answer, but OP does not make a determination to clarify the subject; and without the clarification I won't answer.
Thank you for the discussion.
--SA

:-)