In order to broadcast a custom message you need to create an id for it with the RegisterWindowMessage function, for example:
UINT msg666 = RegisterWindowMessage(L"custom_devil_message");
and use it both in the sending and receiving code:
// sending code
BroadcastSystemMessage(BSF_POSTMESSAGE, &dwRecepients, msg666, 0, 0);
// receiving code
case msg666:
int iClose = 0 + 1;
break;
Remember that messages do not work for console applications.