const                   Constant Data Type Modifier

    This keyword is intended for use in declarations to ensure that the
    object it applies to is not modified or otherwise stored into.
    Specifically, it makes sure that the object is not used as an lvalue.
    This is useful in generating ROMable code; it also provides numerous
    optimization possibilities for the compiler.

      Notes:    The const keyword is a recent addition to the language
                and is not universally supported by compilers.