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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#241

Post by jccalhoun »

ajuc wrote: post #219
bregma wrote: post #168

If you ask people which floor of building they're on, it's going to depend on which country they're in. In North America, at least, the first floor you walk into (in a sane city: I understand there are some which do not qualify in this respect due to hills or historic disaster recovery) is the first floor. On other continents, you enter the ground floor and need to take stairs or an elevating device to get to the fir…

The ground floor is 0. The floor above 0 is 1. The floor below 0 is -1. Anything else is crazy TBH, the whole point of integer numbers is to count things that start at a defined point and go opposite ways. Why shift it and then reinvent weird pseudo-negative numbers like S1? But then again people measure distance in feet and write dates as month day year :)

It would be nice if this was the case. In grad school I taught in a building that was on a hill and had once been separate buildings so different entrances were on different floor and the transition between the former separate buildings was 4 stairs.

So there was a floor with rooms numbered 1xx and 0xx. There was also a floor below the 0xx floor. They just numbered it 00xx. And you could enter the building on any of those floors depending on what door you picked.

The class I taught was in 0005. Room 005 was someone's office. So on the first day of every semester we would have students waiting outside the door of 005 instead of 0005...

Re: Why do arrays start at 0?

#242

Post by RunSet »

jcelerier wrote: post #119
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…

At which number starts the first centimeter on a ruler ?

At which number starts the zeroth centimeter on a ruler?

Re: Why do arrays start at 0?

#243

Post by lupire »

kazinator wrote: post #58
atwood22 wrote: post #37

Earlier quoted context omitted.

No, we don't count from 0. That's like saying we start counting a baker's cup from 0 because you can have half a cup.

The counting activity doesn't begin when the first item is registered; it begins when the counter is initialized to zero. A decision is made to begin counting, along with the realization that nothing has been counting yet. That's when counting has started. When the first item is seen, the counting is then continuing. Suppose your job is to count some events. You check in for work at 8:00 a.m., but the first event has…

Are you sure?

We are talking about the he numbering, not the work-doing.

You start waiting at 8, and you wait between events. But you only count (increment) when an event happens.

The 0 comes for free when you are ready to count (hello golang and C++, as well as human intuition).

When you count stars in the sky you don't say "0, 1, 2".

You say "..., 1, 2", or if no stars show up, you say "there are 0" after timer expires.

Re: Why do arrays start at 0?

#244

Post by smegsicle »

galangalalgol wrote: post #116
yongjik wrote: post #95

Earlier quoted context omitted.

That's why I prefer the Superior(TM) Korean age counting. You are one year old when you're born (it's your first year!). You are two year old on the next New Year's day. (Congratulations, it's your second your now!) So, if you're born on December 31st, you're two years old the next day. (I see no problem, but apparently some people are hung up on such minor details. I can't fathom why.)

Doesn't Korea use the same new year as China? Usually second new moon after winter solstice.

hung up on minor details!

Re: Why do arrays start at 0?

#245

Post by lupire »

8note wrote: post #196
atwood22 wrote: post #148

Earlier quoted context omitted.

No, the mathematical definition of counting (i.e. whether or not a set is countable) involves mapping to the natural numbers, which doesn’t include 0.

Math counting doesn't care where you start. You could start -400 if it's useful for the problem

You can name things however you want, but there is a canonical bijection to zero-based ordinals.

https://en.m.wikipedia.org/wiki/Ordinal_number

Re: Why do arrays start at 0?

#246

Post by bluetomcat »

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…

The "language" that has a 0-based indexing scheme is assembly. An HLL with 1-based counting that compiles to assembly will introduce additional computational overhead for the translation of the index.

If 1-based indexing was used in assembly, then "mov 1(%ebx),%eax" would be the equivalent of "mov (%ebx),%eax".

Re: Why do arrays start at 0?

#247

Post by btilly »

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.

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.

Re: Why do arrays start at 0?

#248

Post by nemetroid »

bluetomcat wrote: post #120
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 disadvantage comes to mind. While the following loop works as expected: for (size_t i = 0; i The following causes an unsigned integer underflow and is an infinite loop: for (size_t i = length - 1; i >= 0; i--) ...

Unless wrapping underflow is sensible for the domain (which it isn’t when representing the size of something), unsigned integers are usually a bad idea.

Re: Why do arrays start at 0?

#249

Post by [deleted] »

bluetomcat wrote: post #120
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 disadvantage comes to mind. While the following loop works as expected: for (size_t i = 0; i The following causes an unsigned integer underflow and is an infinite loop: for (size_t i = length - 1; i >= 0; i--) ...

[deleted]

Re: Why do arrays start at 0?

#250

Post by ziml77 »

bmacho wrote: post #193
kazinator wrote: post #55

Earlier quoted context omitted.

What do you do for a living, and why are they paying you not to understand this?

Can't they just .. disagree? Birthdays are clearly 1 indexed, the first birthday is indexed with 1, and not with 0.

They day you're born is birthday number 0
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