Search item in Listbox As u give i/pin textbox by alphabetic

Question

hiii...

I have a web form which contais listbox with client Names from database and textbox.

Now I want to search a client name in listbox as I type client Name starting letters in textbox, listbox will give me output of that client name. But it should be alphabetically. Means if i type 'R' in textbox then listbox should display all clientname which are starting from 'R', then as i give input to textbox, listbox should give me that output.

help me plz