Thread: SendMessage for any application

Hello
my question is how can send in a text box has an external dialogue
For example, if a chat application, I want to have from my application to pass a message in the text dedicate a seizure

my Code

Code:

HWND handle= FindWindow(NULL,"Name Window");
SetForegroundWindow(handle);
SendMessage(handle, WM_SETTEXT,0,(lParam)"plapla ");

thank you