C++ Primer, Fifth Edition

Like Classes, Enumerations Define New Types

So long as the enum is named, we can define and initialize objects of that type. An enum object may be initialized or assigned only by one of its enumerators or by another object of the same enum type:

open_modes om = 2;      // error: 2 is not of type open_modesom = open_modes::input; // ok: input is an enumerator of open_modes

Objects or enumerators of an unscoped enumeration type are automatically converted to an integral type. As a result, they can be used where an integral value is required:

int i = color::red;   // ok: unscoped enumerator implicitly converted to intint j = peppers::red; // error: scoped enumerations are not implicitly converted