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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#581

Post by btilly »

wizofaus wrote: post #540
btilly wrote: post #428

Earlier quoted context omitted.

The problem is that libraries which assume 0-base break when you have a 1-based array. And vice versa. Trying to combine libraries with different conventions becomes impossible. Therefore changing the base leads to more bugs than either base alone. That said, the more you can just use a foreach to not worry about the index at all, the better. Of 0-based and 1-based, the only data point I have is a side comment of Dij…

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.

Re: Why do arrays start at 0?

#582

Post by nullc »

Maybe my thinking is just warped by the language, but I think 0 indexing is the right thing most-- but not all-- of the time. Looking at my code I have relatively few places where I need to -1 to convert a natural 1 index into a zero index.

It would be easy for languages to offer two array access syntaxes, one for 0 and one for 1 like array[i] for 0 index and array{i} for 1 index access, then the accessing code could use the right tool for the job. Unlike defining the indexing type as a property of an array you shouldn't have problems with accidentally using the wrong one at time of use.

... but to really know if it's a good idea you'd have to test it, and sadly very few concepts in programming are subjected to any kind of rigorous scientific study.

Re: Why do arrays start at 0?

#583

Post by goatlover »

kazinator wrote: post #580
goatlover wrote: post #576

Earlier quoted context omitted.

Or we just start counting with 1, since 1 is the first number we start with. Do small kids start with a concept of zero and then adding one to it, or do they just start at one?

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 miniature unicorns. Since the basket is empty, it could have potentially had anything if we're just going to imagine things in baskets. But we don't enumerate over all possible zero items in the basket. And anyway, the basket isn't really empty since it has N air molecules, N fibers or whatever.

The pedantic point I'm making is that counting at zero is a convention we developed for mathematical reasoning when appropriate, but not a starting place for counting things in everyday language.

Re: Why do arrays start at 0?

#584

Post by lkuty »

biztos wrote: post #536
dathinab wrote: post #530

Earlier quoted context omitted.

Defining index as the element wise offset is a precise well formed definition/name. It's also a definition commonly used in math, through not always. It depends a lot of the area of mathematics and even the cultural context. The only reason we sometimes feel 0-index is wrong IMHO is because the english language describes entities in a sequence as 1st, 2nd, 3rd etc. But I wouldn't be surprised if there is some human l…

Which floor is the first floor in your building? Depends which country your building is in, and more! My apartment building is 1,2… but my mall is G,M,1,2… (same country different architects). For many years I lived in Europe where it’s usually G,1,2… (where G can also be E or Fsz or whatever) and when I was in the US I had to remember that 1 is G, though L,2,3… is also common. City people live with index ambiguity a…

In Belgium (french speaking part of the country, like in France) we call the ground floor (where you enter the buidling) "rez-de-chaussée" (or "rez" for short) which is the equivalent of 0 and then the first floor, numbered 1, is on top of it and you use an elevator or stairs to reach it.

Re: Why do arrays start at 0?

#585

Post by bee_rider »

Yujf wrote: post #232
bee_rider wrote: post #9

Earlier quoted context omitted.

The mental model of being an offset to a memory address is, I think, part of it. I'd be surprised if the use of zero vs one actually made any difference, from a number of operations point of view -- from the compiler's point of view, the first element in the array is the first element in the array, no matter what we call it. I mean in an extreme edge case maybe if you are computing an index, and it happens to be zero…

How would it not make a difference? If you calculate an index at runtime, to get access to the element, in 0 based would be pointer + index. In 1 based it is however pointer + index - 1 clearly there is an extra subtraction there? In x86 you could probably hide it in the addressing but that does not mean it does not to be computed

One option, at least, would be for malloc and friends to return pointer-1, rather than pointer. That said, I'm sure a compilers expert could come up with a much better option.

Re: Why do arrays start at 0?

#586

Post by goatlover »

anigbrowl wrote: post #305

I may think that counting 0 as a natural number makes a lot of math more elegant, but clearly I’m just too dumb to rise to the level of wrong. fruits = ['apple'] \\ Hello I have fruits x = len(fruits) \\ Only one kind tho lol fruits[x] \\ OK here is what I have SUBSCRIPT OUT OF RANGE I have always hated zero indexing for this reason (other than thinking in assembler where it is beautiful). It is of course useful in m…

Also, considering that Python uses -1 for indexing the last element, instead of -0, which means the last element is not an offset when using negative indices.

Re: Why do arrays start at 0?

#587

Post by smeagull »

Because indexing happens with integers. Back then space was a concern, so you'd use unsigned integers, and those start with zero. Internally they'll all be using offsets, and its easier to not do a conversion, than to do a conversion.

Re: Why do arrays start at 0?

#588

Post by smeagull »

tuatoru wrote: post #516
xg15 wrote: post #235

I don't quite understand the argument "0-based being easier for pointer arithmetic is nonsense because the language doesn't have pointers". Whether or not the language presents the concept of "pointer" to the user is independent of whether or not it uses pointers internally. And if it exposes arrays as a concept, it has to implement them somehow. The simplest possible implementation of arrays is having a start addres…

I would be fine with it all if 0-based was called "offset", with "index" reserved for 1-based. The element at offset 0 is the first element. Precision in naming is important.

> Precision in naming is important.

It really isn't. The human race gets by without it the vast majority of the time.

Re: Why do arrays start at 0?

#589

Post by lokedhs »

Someone wrote: post #351
xg15 wrote: post #235

I don't quite understand the argument "0-based being easier for pointer arithmetic is nonsense because the language doesn't have pointers". Whether or not the language presents the concept of "pointer" to the user is independent of whether or not it uses pointers internally. And if it exposes arrays as a concept, it has to implement them somehow. The simplest possible implementation of arrays is having a start addres…

> To get the address of a particular item, this layout naturally leads to the formula "base address + index * element size", with "index" being 0-based. If you want to expose other indexing schemes in your language, you'll have to add more logic to convert the user-visible index back to 0-based before you can obtain the address. The easy way to do that is by shifting the base address. In pseudo-C (I think that comput…

This is undefined behaviour, as a pointer is only allowed to point to valid addresses (as well as the index of the last element + 1, but it can't be dereferenced).

Re: Why do arrays start at 0?

#590

Post by smeagull »

Someone wrote: post #351
xg15 wrote: post #235

I don't quite understand the argument "0-based being easier for pointer arithmetic is nonsense because the language doesn't have pointers". Whether or not the language presents the concept of "pointer" to the user is independent of whether or not it uses pointers internally. And if it exposes arrays as a concept, it has to implement them somehow. The simplest possible implementation of arrays is having a start addres…

> To get the address of a particular item, this layout naturally leads to the formula "base address + index * element size", with "index" being 0-based. If you want to expose other indexing schemes in your language, you'll have to add more logic to convert the user-visible index back to 0-based before you can obtain the address. The easy way to do that is by shifting the base address. In pseudo-C (I think that comput…

Okay, now do 2D arrays.
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