An application can use several types of secondary windows: frame windows, client windows, control windows, dialog windows, message boxes, and menus. Typically, an application's main window consists of several of these windows acting as one.
A frame window is a window that an application uses as the base when constructing a main window or other composite window, such as a dialog window or message box. (A composite window is a collection of windows that interact with one another and are kept together as a unit.) A frame window provides basic features, such as borders and a menu bar. Frame windows have a set of resources associated with them. These include icons, menus, and accelerators (shortcut keys to the user), which, typically, are defined in an application's resource file.
A dialog window is a frame window that contains one or more control windows. Dialog windows are used almost exclusively for prompting the user for input. An application usually creates a dialog window when it needs additional information to complete a command. The application destroys the dialog window after the user has provided the requested information.
A message box is a frame window that an application uses to display a note, caution, or warning to the user. For instance, an application can use a message box to inform the user of a problem that the application encountered while performing a task.
A client window is the window in which the application displays the current document or data. For example, a desktop-publishing application displays the current page of a document in a client window. Most applications create at least one client window. The application must provide a function, called a window procedure, to process input to the client window and to display output.
A control window is a window used in conjunction with another window to perform useful tasks, such as displaying a menu or scrolling information in a client window. The operating system provides several predefined control-window classes that an application can use to create control windows. Control windows include buttons, entry fields, list boxes, combination boxes, menus, scroll bars, static text, and title bars.
A menu is a control window that presents a list of commands and other menus to the user. Using a mouse or the keyboard, the user can select a task; the application then performs the selected task.