Quotes About Const

The keyword const doesn't turn a variable into a constant! A symbol with the const qualifier merely means that the symbol cannot be used for assignment. This makes the value read-only through that symbol ; it does not prevent the value from being modified through some other means internal (or even external) to the program.

The const specifiers on the functions returning the real and imaginary parts indicate that these functions do not modify the object for which they are called.