How to display text in next line in multiline textbox?

    use characters like this as example this for windows application:

string newline1 as string;
newline1 = char(13)+char(10);
'giving values with new line
textbox1.text="First Line" + newline1;
textbox1.Text +="Second Line" + newline1;
textbox1.Text +="Third Line";
'newline1 acts as Enter in this case

but if you mean in web application it is like "Mohamed El Baz" said:

textbox1.Text = "First Line";

textbox1.Text +="<br>Second Line" ;

textbox1.Text += "<br>Third Line";