how to insert char/string into a text box of current window

hey

my code implements virtual keyboard that inserts chars into the text edit (text box).
i want to insert the same char into a text box of the current window running such as facebook, search engines ...

(I'm not sure but i think that i need to add some system liberies in order to interupte as a keyboard)

please help.

You need to use system specific APIs to stuff characters into the operating system input stream for other applications. SendMessage() with appropriate window handles will get you some of the way.