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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#591

Post by lokedhs »

wizofaus wrote: post #336
mananaysiempre wrote: post #179

Earlier quoted context omitted.

A rare case where 1-based indexing is more convenient is complete binary trees laid out breadth-first (as in a standard binary heap): parent is i div 2 and children are 2i and 2i+1 when starting at one and who knows what when starting at zero. But that’s the only one I know.

Except 1-based indexing is what we use in normal language. We don't use "zeroeth" or "player (number) zero" etc. And the word "first" is shortened to 1st etc. Personally I think we'd be better off if programming languages stuck to the same convention - off-by-1 errors aren't the hardest problems to deal with but they're still annoying.

That's confusing ordinal and cardinal numbers. The element with index 0 is the first number. The element with index 1 is the second number, and so on.

Using the term "zeroth" is basically some form of showing off (even though it's kinda fun), but will be utterly confusing when you get to the fifty-second element which is the last in a group of 53 elements.

Re: Why do arrays start at 0?

#592

Post by ehvatum »

empiricus wrote: post #262
xxs wrote: post #137

Earlier quoted context omitted.

the correct way/idiom to reverse iterate an array is for (size_t i = length; i-- > 0; )... It's surprising how often the issue pops, it works well with both signed and unsigned integers. (edit) I've started with one based indexing (basic)... mixed with 0 based (assembly), more 1 based (pascal), then more stuff (all zero based). I am, yet, to see a real advantage of a one based indexing... after the initial process.

Is this cache friendly?

It is not, unless your compiler is smart enough to recognize reverse iteration and prefetch appropriately.

If performance matters, you should experiment with __builtin_prefetch, which is available in clang and GCC.

Re: Why do arrays start at 0?

#593

Post by kazinator »

goatlover wrote: post #583
kazinator wrote: post #580

Earlier quoted context omitted.

If you start at 1, how do you answer the question "how many apples are in the basket", when the basket is empty? Or do you believe that the answer "none" or "zero" is then given without the activity of counting having taken place? What do we call the meta-activity then: the procedure that results either in the "empty" answer or "one", "two"? Whatever that activity is called, it starts with a concept of zero. Let's ca…

Humans could do basic counting prior to the concept of zero. Obviously kids or anyone prior to zero would say there are no apples in the basket, but if you were to ask an ancient Greek philosopher if that meant "no apples" is something worthy of being denoted, they might think you're doing sophistry and trying to elevate nothing to something. A smart ass kid might reply there are zero oranges in the basket, or zero m…

If an ancient Greek philosopher had three apples in his basket, and I took them away while he wasn't looking, oh, he would definitely find "no apples" something worthy of being denoted.

Re: Why do arrays start at 0?

#594

Post by ChrisRackauckas »

btilly wrote: post #581
wizofaus wrote: post #540

Earlier quoted context omitted.

I'd expect the compiler not to let you to pass a 0-based array to a library function expecting a 1-based array. I'm pretty sure that's how it worked with Visual Basic, which was the only language I ever used such a feature in.

You are demanding a lot from the type system. Search for OffsetArrays in https://yuri.is/not-julia/ for practical problems encountered in trying to make this feature work in a language whose compiler does try to be smart.

The type system does tell you if this is used. `::OffsetArray`.

Re: Why do arrays start at 0?

#596

Post by froh »

maxdamantus wrote: post #504
Jtsummers wrote: post #444

Earlier quoted context omitted.

If you did this, you'd subtract one once at array creation. Or subtract whatever the offset is (really, you'd subtract 1 * data type size). Under the hood, using C syntax instead of assembly: int foo[n]; // what the user wrote // what happens behind the scenes, after a fashion int* foo = malloc(n * sizeof(int); // or sp - n * sizeof(int) if stack allocated; subtraction since stacks usually grow "down" foo = foo - 1;…

Since as you say, C doesn't carry size information, you would actually need to do it each time a pointer is created from an object. In C you can have arrays of arrays (not pointers) or arrays in structs, where there is no pointer on creation: // 11 arrays are created here int foo[10][10]; It doesn't make sense to create pointers for the 10 inner arrays, so the subtraction would presumably happen when referring to eac…

when I count apples I happily start with one. it's "natural" to label the first thing "1".

or how would you count, say, 3 Apples? or three legionaries?

Re: Why do arrays start at 0?

#598

Post by ehvatum »

sgtnoodle wrote: post #333
empiricus wrote: post #262

Earlier quoted context omitted.

Is this cache friendly?

Sure, why wouldn't it be? As far as a cache is concerned, I don't think reverse sequential iteration would be any different than forward sequential. The actual RAM accesses may be less optimal if there's some speculative pre-fetching with assumed forward sequential access, but that's conjecture.

With some exceptions, hardware prefetch works in terms of ascending accesses. To learn if a particular CPU will prefetch for descending access, benchmarking is essential. Best to use soft prefetch calls if performance is critical.

Re: Why do arrays start at 0?

#599

Post by lokedhs »

pvinis wrote: post #567
chii wrote: post #564

Earlier quoted context omitted.

but nobody "says" zero o'clock - it's always twelve o'clock! and the example is in 24hr format - which needs to have the 00 to differentiate it from being 12:30. But if you write in 12hr format, you don't ever use 00 - it's always 12:30am or 12:30pm

First of all, you don't. Or I guess most Americans don't. I do, or most Europeans do. 12.30am and 12.30pm feels just very wrong in Europe. But yea, I do agree with you. we don't say 0, we say 12, no matter if it's noon or midnight. That's because we humans avoid saying zero when we mean zero. It's the same with other comments here, talking about counding seconds, we say "ok go, one, two,.. and not "zero, one, two,.."…

I'm from Sweden, and I certainly would say 00:15 (as zero fifteen). Although the time at exactly 00:00 would be called midnight.

Re: Why do arrays start at 0?

#600

Post by lokedhs »

pygy_ wrote: post #440
anigbrowl wrote: post #425

Earlier quoted context omitted.

Quoted post unavailable.

Anecdotally, I taught my children numbers starting from zero with a similar routine, based on cardinality. They immediately got it. My kids' school also uses zero-based tables. "Natural" is a very loaded and ambiguous term, best avoided if you hope to have sane discussions.

The index is the distance away from the first element. So index 0 is the first element. Index 3 is 3 away from the first element, so the fourth element.

It's the difference between ordinal and cardinal numbers. In other words, counting and indexing.

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