c# - RichTextBox delete old output, and set new output when clicking a button -

in c# project have read-only richtextbox, textbox input , button. when user types text, output written in richtextbox when push button.

but if type more text, old text still in richtextbox , new text appended.

how can delete old output clicking button , @ once indicate new output?

thank indeed!

-valeria-

string newstring =txtinput.text; richtextbox.text+=newstring;