When you create a control, you give it a unique identifier, or control ID. You specify the control ID when you create the control. To do so, include the control ID as the hMenu parameter for the CreateWindow function. The control supplies the control ID in any notification message it sends to the window function of the parent window. The control ID is especially useful if you have several controls in a window. It is the quickest, easiest way to distinguish one control from another.