A control is a child window an application uses in conjunction with another window to perform simple input and output (I/O) tasks. Controls are most often used within dialog boxes, but they can also be used in other windows. Controls within dialog boxes provide the user with the means to type text, choose options, and direct a dialog box to complete its action. Controls in other windows provide a variety of services, such as letting the user choose commands, view status, and view and edit text.
Controls, like other windows, each belong to a window class, either predefined or owner-defined. The window class and the corresponding window procedure define the properties of the control, its appearance, behavior, and purpose. An application can create controls individually by specifying the name of the window class when calling the CreateWindowEx function. An application can also direct the system to create controls for a dialog box by specifying the controls in the dialog box template.