Terminate an another application

[local external function declaration]
FUNCTION ulong FindWindowA(ulong classname, String windowname) & 
  LIBRARY "user32.dll"
FUNCTION boolean PostMessageA&
  (ulong hwndle,UINT wmsg,ulong wParam,ulong lParam) & 
  LIBRARY "user32.dll"
  
  
[powerscript]
CONSTANT uint WM_QUIT = 18 // hex 0x0012
ulong     lul_handle
string    ls_app

ls_app = "Calculator"
//  ls_app = "Calculatrice"  in french windows!

lul_handle = FindWindowA(0, ls_app)

IF lul_handle > 0 THEN 
   PostMessageA(lul_handle, WM_QUIT, 0, 0);
ELSE
   MessageBox("Oups", ls_app + " is not running!")
END IF