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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#351

Post by Someone »

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 computing the b pointer is non-conforming, even if the code never tries to access b[0], but compilers can do this without problems):

   int a[100];      // array of 100 integers, zero-based
   int * b = a - 1; // array of 100 integers, one-based
Things only get costly when you want to check array bounds or when you have multi-dimensional arrays. There also may be non-standard architectures where this kind of stuff isn’t possible.

Re: Why do arrays start at 0?

#352

Post by gitonthescene »

blueflow wrote: post #269
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…

That so people in this thread argue about the higher-level language (missing the point) shows that few people found access to the underlying machine code. Which is sad, because all code is still executed as machine instructions even when the developer does not see it or does not want to care.

It was just most basic example. Indices are connected with math all the time. Consider implementing circular queues with 1-based arrays. Any arguments about what’s _possible_ miss the point. Arguments about what _feels_ natural purport to know the human mind which I find generally suspect. Mostly I think of computers as tools and am interested in getting the most functionality out as smoothly as possible not as slaves whose job it is to make my life worry free.

Re: Why do arrays start at 0?

#353

Post by btilly »

wizofaus wrote: post #338
tabtab wrote: post #205

Earlier quoted context omitted.

In many domains code maintenance is more important than hardware costs. In many domains 1-based indexing is a better fit, meaning less conversion code, meaning simpler code. Thus, the best indexing choice depends on the domain and circumstances, as do many controversial questions. Most tend to specialize in specific kinds of domains and over-extrapolate their experience into other domains.

I'd agree so why did languages that allow specifying the base die (other than maybe VBA).

Because changing the base is a great source of bugs.

That said, not all languages have given up on this. For example Julia allows it. https://docs.julialang.org/en/v1/devdocs/offset-arrays/

Ironically I learned this from a discussion of Julia bugs. Apparently changing offsetting of arrays has proven to be a source of bugs in Julia. So maybe someday they will come to the same conclusion as languages like Perl and stop allowing it.

Re: Why do arrays start at 0?

#354

Post by ellen364 »

randomdata wrote: post #19
hougaard wrote: post #14

It really comes down to a choice between a machine-focused (0) or human-focused (1) approach. The 0 makes a lot of sense in a C pointer world where memcpy and other alike functions can be written very thight. The 1 makes a lot of sense in a human world, when we count, we start at 1, we talk about the "1st", counting on finger starts with 1, etc. I once were at a Lua (1 indexed language) conference where this was disc…

> when we count, we start at 1, we talk about the "1st" Although often with an implicit zero. Under typical North American culture, your 1st birthday, for example, is more accurately the first anniversary of your birthday. Your birth is zero indexed.

Demographers sometimes describe age as “the number of completed years”, which always struck me as a wonderfully simple explanation.

Re: Why do arrays start at 0?

#355

Post by bitwize »

dhosek wrote: post #342

When he talked about BASIC having 1-based arrays, I had to check my memory against online AppleSoft BASIC documentation and indeed, AppleSoft, at least did have 0-based arrays.¹ I also had to check on Pascal which I haven’t written anything significant in for some 20 years and it turns out that by default, Pascal arrays are 1-based, but most of the code that I worked with (which tended to have its roots in Knuth-writ…

Most of the BASICs I remember had 0-based indexing by default. But you could change this with the statement OPTION BASE 1 at the top of your program.

This was true of even TI-99/4A BASIC, which was closer to Dartmouth BASIC and not written by Microsoft.

Re: Why do arrays start at 0?

#356

Post by randomdata »

anigbrowl wrote: post #331
randomdata wrote: post #308

Earlier quoted context omitted.

If no apples is the unusual state, like you expected to find an apple in your lunchbox but someone ate it without your knowledge, then certainly there would be reason to communicate the no apples state. It is ignored in communication when it does not provide useful information, but it is not forgotten. The 0th index is implicitly there.

Come to the infinity store - we literally sell everything! (some items may be out of stock)

Yes, the infinite state is also implicitly found within the state set. Conveniently found at the infinity index.

Re: Why do arrays start at 0?

#357

Post by marak830 »

anigbrowl wrote: post #311
divbzero wrote: post #283

Earlier quoted context omitted.

The same applies to counting in other bases too. For instance, in 1-indexed counting grids for kids, the last column always feels out of place. 0-indexed decimal grid: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 8…

Are you sure it doesn't just look that way because you are used to monospaced fonts? Ask a kid to show you their zeroth finger.

I asked my son to show me zero fingers(after show me 2 fingers and 5 fingers), he closed his fists.

Re: Why do arrays start at 0?

#358

Post by ryanisnan »

juped wrote: post #339

Zero-based indexing is always wrong; an ordered collection of things does not have a zeroth thing. Sometimes you have a data structure called an "array", which means "a bunch of things that are the same size next to each other in memory". You can store the address of the whole array as the address of its first element, and offset into it by an offset; clearly, the offset of the first element is zero, but it's not the…

I hate to break it to you but natural spoken language is not a fixed concept, words can have many meanings and interpretations, and those meanings and interpretations can mean different things to different people at different times.

Because you predominantly think of indexing as the first definition as shown here[1], does not mean everyone else does. Be careful when using absolutes, especially when talking about languages.

[1] - https://www.merriam-webster.com/dictionary/index

Re: Why do arrays start at 0?

#359

Post by anigbrowl »

marak830 wrote: post #357
anigbrowl wrote: post #311

Earlier quoted context omitted.

Are you sure it doesn't just look that way because you are used to monospaced fonts? Ask a kid to show you their zeroth finger.

I asked my son to show me zero fingers(after show me 2 fingers and 5 fingers), he closed his fists.

My point exactly - there isn't an identifiable zeroth finger.

Re: Why do arrays start at 0?

#360

Post by layer8 »

Jtsummers wrote: post #341
layer8 wrote: post #334

Earlier quoted context omitted.

It matters whenever you need to process a proper subrange of an array, and that shouldn’t be different from when the subrange happens to be the whole range. It’s simpler if the same convention is used in all cases. E.g. in Java, a typical example is that OutputStream has the following two methods, where the first can delegate to the second, and the second (which write the specified subrange of the array) can easily c…

I addressed that: > If we let the initial offset float, then the inclusive-exclusive makes sense. But you replied to someone using inclusive-inclusive for 1-based arrays and complained about the delta not matching the length. Which is a nonsensical complaint, you have the length already why would you need to calculate anything?

In case of the subrange you don’t have the length (or you conversely have the length but not the upper bound), and you don’t want to use different conventions based on whether you process the subrange or the whole range. I’m not sure how I can make it clearer.
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