Actually what's funny here is that (index - 1) % N doesn't work in C, as it can be negative. You have to use (index+N-1) % N.

I still prefer 0 based indexing (for example for calculating the size of an array), but the worst thing is inconsistency between languages. 0 won, that's it.

Oh, that's hilarious. I tested this in Python where it worked fine and forgot that C has a "broken" modulo operator:

Python:

  >>> -1 % 20
  19

C:

  printf("%d\n", (-1 % 20));
  -1

Even worse, it still fails even on unsigned:

  printf("%d\n", ((unsigned int)0 - (unsigned int)1) % 20);
  15

So you still need to add N:

  printf("%d\n", ((unsigned int)0 - (unsigned int)1 + 20) % 20);
  19

Thanks for the reminder of humility.

(Side Note: For those reading this, the C operator isn't "broken", per se. There are three properties that modulo can adhere to but two of the three are mutually exclusive.)

C does not have a modulo operator. It has a remainder operator, which works perfectly fine. Calling C's `%` a 'broken modulo operator' is like calling `+` a 'broken minus operator'. Quite a few languages have separate operators, keywords, or functions for 'modulo' and 'remainder'.

> We rarely operate on ranges, but we operate on offsets all the time.

I would disagree with that assertion. Maybe it was true historically, but just look at how often ranges are used today - the fact that many languages have an abstraction for them in the core library is a testament to that.

I would also argue that having ranges (and underlying iterators) as opaque abstractions is preferable to conflating them with indices. Then you can have your cake and eat it too - the elements are counted naturally, but if you have an iterator to the first element, you can deal with 0-based offsets just as naturally.

Could also be that C is superior in other ways, there isn't really a big difference between 0 and 1 based indexing, and thus 0 based won on the back of Cs other strengths.

The Dijkstra discussion is only aesthetic preference, nothing more.

Edit:

In Julia the examples would also idiomatically be written in terms of the provided mod1 function:

    new_index = mod1(old_index + 1, N)
    new_index = mod1(old_index - 1, N)

> Could also be that C is superior in other ways, there isn't really a big difference between 0 and 1 based indexing, and thus 0 based won on the back of Cs other strengths.

Possibly, but then 1-based indexing certainly isn't enough of a positive to overcome the other stuff. And that's evidence, too.

> The Dijkstra discussion is only aesthetic preference, nothing more.

Dijkstra's comment says that people using the other 3 conventions were committing more errors--that's data.

> In Julia the examples would also idiomatically be written in terms of the provided mod1 function:

Agreed. The proper way is to encapsulate that behind a function so you don't have to think about it.

However, if you have to unpack that and repack it all the time (for example, Lua calling C), then you can't just encapsulate and forget about it.