This works for me:

#DEFINE WM_CLOSE   0x10
DECLARE LONG FindWindow IN User32 ;
	STRING cClassName, STRING cWindowTitle
DECLARE LONG SendMessage IN User32 ;
	LONG HWND, LONG Msg, LONG wParam, LONG LPARAM

HWND = FindWindow( NULL, 'Calculator')
IF HWND > 0
	SendMessage( HWND, WM_CLOSE, 0, 0 )
ENDIF
RETURN

>I try to close another Application eg. Ms Calculator by using API call. I try the following code but it does not work.
>
>
>
>DECLARE INTEGER FindWindow ;
> IN WIN32API STRING cNull,STRING cWinName
>
>
>DECLARE INTEGER SendMessage IN user32;
> INTEGER hWnd,;
> INTEGER Msg,;
> INTEGER wParam,;
> INTEGER lParam
>
>
>mWinHandle = FindWindow(0,'Calculator')
>IF mWinHandle > 0
> SendMessage(mWinHandle,10,0,0)
>ELSE
> MESSAGEBOX(mWinHandle)
>ENDIF