How can I use EN_UPDATE or some similiar command to
preview the letter that I typed before it is displayed in the edit
box and how can I not let certain letters be displayed in an edit
box, like the letter h, or the letter z? That is, if the user's cursor
was in edit_box1 and typed the letter h, nothing is displayed
in the editbox.

Any response any one can give me will be greatly appreciated.