Long before C++ was created, C was the language used to develop the Windows operating system and Windows programs. Thousands of existing programs for Windows are written in C. For this reason, MFC was created on top of the Win32 API, with many of the classes acting as a wrapper around Win32 API functions. For example, there is a collection of Win32 API functions with a handle to a window as a parameter. Because these are behaviors of a window, a CWnd class was created in MFC that contains these API functions as members. In other words, invoking a member function of the CWnd class eventually invokes an appropriate C function in the Win32 API.