Re: Modular type. What is it and why?

["Mike Silva" <mjsilva@jps.net>]

Ole-Hjalmar Kristensen wrote in message ...
>> but you can't do:
>>
>>  index = ( index - 1 ) % NUM_ELEMENTS;    /* won't handle 0 ->
>> NUM_ELEMENTS - 1 correctly */
>
>Actually, if index is unsigned, then it *will* handle 0 ->
>NUM_ELEMENTS - 1 correctly.

No, if you roll e.g. a 16 bit unsigned int from 0 to 65535, the value 65535
mod N will not in general be N - 1, as we want.  (e.g., by inspection, 65535
mod 10 is 5)
>
>> As Ole-Hjalmar Kristensen commented, the nice Ada solution doesn't work
if
>> NUM_ELEMENTS varies at runtime (at least, it appears that a modular type
>> can't be defined dynamically -- correct?), but that's not the usual case
>> I run across.
>
>Agreed, I just thought I would mention it.

Actually, the more I thought about it the more the static limitation on
modular types makes my idea worthless.  Even if NUM_ELEMENTS is static for
each menu, I'd want the same routine to handle multiple menus, each with a
different NUM_ELEMENTS.  Oh well...

Mike