built, that is, a window whose resources have been specified. If you do not specify these resources, that is, if you pass the lpszClassName argument as NULL , the compiler would use internal default values for the window. These default are: a window that can be redrawn when the user moves or resizes it, a white background for the main area of the window, the arrow cursor, and the Windows "flat" icon, called IDI_APPLICATION . To use your own resources, you must first create then register them. To register the resources, you can call the AfxRegisterWndClass() global function. Its syntax is: LPCTSTR AFXAPI AfxRegisterWndClass(UINT nClassStyle,