What does MessageBox return?
Return value
If a message box has a Cancel button, the function returns the IDCANCEL value if either the ESC key is pressed or the Cancel button is selected. If the message box has no Cancel button, pressing ESC will no effect - unless an MB_OK button is present.
What is message box class?
A message box is a prefabricated modal dialog box that displays a text message to a user. You show a message box by calling the static Show method of the MessageBox class. The text message that is displayed is the string argument that you pass to Show.