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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#331

Post by anigbrowl »

randomdata wrote: post #308
lupire wrote: post #270

Earlier quoted context omitted.

If I care about apples (for my lunch, or my store), I care about the difference between having 0 of them and not having bothered to count yet. 0!=null

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)

Re: Why do arrays start at 0?

#332

Post by Uptrenda »

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…

This is far easier and clearer than the entire article. Good stuff.

Re: Why do arrays start at 0?

#333

Post by sgtnoodle »

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?

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.

Re: Why do arrays start at 0?

#334

Post by layer8 »

Jtsummers wrote: post #310
layer8 wrote: post #285

Earlier quoted context omitted.

Then the delta of both bounds (N – 1) wouldn’t equal the length of the range (N). The inclusive-exclusive convention is used in order for `end = start + length` to hold.

Why does that matter when the starting point is 1? In that case, you don't need the delta because you have the length already. In the case of a 0-based range you also don't need the delta, though you will want to use the inclusive-exclusive convention so that you get the length "for free". 1 You only calculate the length when dealing with other than 0- or 1-based ranges. There, the inclusive-exclusive convention is v…

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 calculate the number of bytes to write:

  int write(byte[] bytes)
  {
      return write(bytes, 0, bytes.length);
  }

  int write(byte[] bytes, int start, int end)
  {
      int length = end - start;
      ...
  }

Re: Why do arrays start at 0?

#335

Post by anigbrowl »

Stratoscope wrote: post #85
randomdata wrote: post #19

Earlier quoted context omitted.

> 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.

Rulers too. A ruler starts at 0, not 1.

That's because it's dimensional. How long is the shortest possible ruler?

Re: Why do arrays start at 0?

#336

Post by wizofaus »

mananaysiempre wrote: post #179
twanvl wrote: post #45

Other advantages of zero based indexing, beyond being 'closer to the machine': It works better with the modulo operator: `array[i%length]` vs `array[(i+length-1)%length+1]`. Or you would have to define a modulo-like operator that maps ℕ to [1..n]. It works better if you have a multi-dimensional index, for example the pixels in an image. With 0 based indexing, pixel `(x,y)` is at `array[x+width y]`. With 1 based index…

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.

Re: Why do arrays start at 0?

#337

Post by systemvoltage »

jwarden wrote: post #296
systemvoltage wrote: post #255

Earlier quoted context omitted.

I've been living in North America for decades. Every building has G (zero). This is the floor that you walk into and has a lobby. The next floor up is 1 as such is labeled in the elevator. So your initial assumption is incorrect from my experience.

What city are you in, out of curiosity?

SF Bay Area (currently), but have lived in several major metro areas.

Re: Why do arrays start at 0?

#338

Post by wizofaus »

tabtab wrote: post #205
twanvl wrote: post #45

Other advantages of zero based indexing, beyond being 'closer to the machine': It works better with the modulo operator: `array[i%length]` vs `array[(i+length-1)%length+1]`. Or you would have to define a modulo-like operator that maps ℕ to [1..n]. It works better if you have a multi-dimensional index, for example the pixels in an image. With 0 based indexing, pixel `(x,y)` is at `array[x+width y]`. With 1 based index…

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).

Re: Why do arrays start at 0?

#339

Post by juped »

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 "zeroth" element.

And finally, sometimes you have cargo cult behavior by people who think that the way offsets into arrays work is because "numbering starts at zero in computers!" or some similarly wrong rationalization. This is when you get stupid things like (nth 0 list) in a lisp.

Re: Why do arrays start at 0?

#340

Post by btilly »

JadeNB wrote: post #297
btilly wrote: post #247

Earlier quoted context omitted.

With 0-based indexing the children are at 2i+1 and 2i+2. The parent is at (i-1) div 2. Not hard to figure out.

> With 0-based indexing the children are at 2i+1 and 2i+2. The parent is at (i-1) div 2. > Not hard to figure out. While that's true, "you just shift by 1" is equally good at all arguments for or against 0-based indexing, so deploying it here probably won't convince.

I was not trying to convince.

That said, the effort of one versus the other is so trivial that there is no point in ever using effort as an argument either way. Doubly so because what seems like effort to us is simple unfamiliarity.

What is important is which one leads to more careless errors in practice. As a trivial example, consistent indentation takes effort, but failing to do it leads to more careless errors. Therefore everyone indents code.

The only data point I've seen on that is the side remark about Mesa in https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/E.... That remark, therefore, is the only argument that I care about.

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