Dialog boxes are either ”modal“ or ”modeless.“ The modal dialog box is the most common. When your program displays a modal dialog box, the user cannot switch between the dialog box and another window in your program. The user must explicitly end the dialog box, usually by clicking a push button marked either OK or Cancel. The user can, however, generally switch to another program while the dialog box is still displayed. Some dialog boxes (called ”system modal“) do not allow even this. System modal dialog boxes must be ended before the user does anything else in Windows.