Why do arrays start at 0? • Hacker News Board

Re: Why do arrays start at 0?

#561

Post by pvinis » Thu, Aug 25, 2022, 2:46 AM UTC

wruza wrote: post #451

throwaway821909 wrote: post #218

Earlier quoted context omitted.

It helps that change happens particularly fast at that age, so the difference between newborn and 6 months is worth mentioning. Later on the units go up again and we just say "I'm in my 30s" :P On the other hand a computer/car/house can also be 10 years old but not 0.

On the other hand a computer/car/house can also be 10 years old but not 0 Really? When I buy a new PC, to me it will get 1 year old only after a year. Before that it is just NEW. Is that what you meant?

Exactly. What we call "new" is the 0th year. It's the same when you start counting seconds. You say "ok counting starts now", then wait a second and say "one", then wait and say "two". Before you say "one", you don't say zero, but it's implied by you waiting a second after you or someone says "go". That's still 0-indexed.

Re: Why do arrays start at 0?

#562

Post by chii » Thu, Aug 25, 2022, 2:48 AM UTC

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.

i would suspect that the cache prefetch/prediction could use the "velocity" of the memory access to predict the next access; so if the access pattern was going backwards, the "velocity" would be negative, but prefetching would still work if they just followed the predicted pattern.

Re: Why do arrays start at 0?

#563

Post by Grazester » Thu, Aug 25, 2022, 2:50 AM UTC

rmason wrote: post #164

Actually in not all languages do arrays start at 0. In ColdFusion for example arrays start at 1. I've never been able to receive a reason as to why CF's original author, J.J. Allaire, did it that way.

Came here to say this about CF. I work in Coldfusion but coming from a background of other languages I would always reference 0 as the start of an array. This was the source of countless errors for me until I got use to it.

Re: Why do arrays start at 0?

#564

Post by chii » Thu, Aug 25, 2022, 2:52 AM UTC

pvinis wrote: post #555

OscarCunningham wrote: post #389

Earlier quoted context omitted.

I think the 1-indexing folks would have to argue that a%b should return a value from 1 to b inclusive. This does make the same sort of intuitive sense as 1-indexing. For example we number clocks from 1 to 12.

No we don't. Clocks start at 0. what time is it when it's half an hour after midnight? 00:30.

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

Re: Why do arrays start at 0?

#565

Post by Grazester » Thu, Aug 25, 2022, 2:52 AM UTC

rmason wrote: post #164

Actually in not all languages do arrays start at 0. In ColdFusion for example arrays start at 1. I've never been able to receive a reason as to why CF's original author, J.J. Allaire, did it that way.

Came here to say this about CF. I work in Coldfusion but coming from a background of other languages I would always reference 0 as the start of an array. This was the source of countless errors for me until I got use to it.

My manager thinks it was done to make the language easier to understand for people just getting into programming.

Re: Why do arrays start at 0?

#566

Post by Morgawr » Thu, Aug 25, 2022, 2:58 AM UTC

Octoth0rpe wrote: post #197

LudwigNagasena wrote: post #115

Earlier quoted context omitted.

Do people not study grammar in American schools? I thought all kids learn the distinction between cardinal (one, two, three) and ordinal (first, second, third) numbers.

The English grammar that Americans study in school is likely somewhat different than the English grammar that is taught outside of America as the goal of the latter is likely focused on helping students map their native language onto English. I would agree that `ordinal` is uncommon word for many Americans, but it wouldn't at all surprise me if there were languages where the equivalent word was far more common, and t…

> The English grammar that Americans study in school is likely somewhat different than the English grammar that is taught outside of America as the goal of the latter is likely focused on helping students map their native language onto English

English is spoken as a native language in many countries outside of America.

Re: Why do arrays start at 0?

#567

Post by pvinis » Thu, Aug 25, 2022, 2:59 AM UTC

chii wrote: post #564

pvinis wrote: post #555

Earlier quoted context omitted.

No we don't. Clocks start at 0. what time is it when it's half an hour after midnight? 00:30.

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,..". We say 3 months old baby, and not 0 years old baby.

We use 0-index in so many things, we just avoid saying the word "zero", and we use other names or other units to avoid that word.

Re: Why do arrays start at 0?

#568

Post by JadeNB » Thu, Aug 25, 2022, 2:59 AM UTC

salty_biscuits wrote: post #494

JadeNB wrote: post #471

Earlier quoted context omitted.

I'm a mathematician, and 0-based indexing makes way more sense to me. Dijkstra's argument ( https://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF ) is that we count the number of predecessors. This fits well with the mathematical usage, at least among mathematicians who care to dig into the order-theoretic foundations: the von Neumann construction of ordinals (and of cardinals as least ordinals of a fixed, well, car…

I'm a mathematician too, and it doesn't make sense to me. It seems somewhat arbitrary depending on the application, i.e. I think it is a type problem. We use an Int to mean something special about array elements. I'd be happier with first() and last() methods really, I don't care for coming up with meanings based on implementation details.

> I'm a mathematician too, and it doesn't make sense to me.

Just to be clear, I wasn't making some sort of bizarre appeal to authority; whether something makes sense is a matter of taste, not of mathematics, and can't be proven or dis-. I meant only to respond to:

> In maths they always talk about the first element in a vector, not the zeroth. It is a bad argument to point to mathematics for using zero based indices.

I don't know for sure which convention is more common, though I suspect you're right that it's the 1-based convention, but I do know that it's false that 'they'—meaning, among others, we!—always talk about the first element/component in a vector. I probably will do that in a first Linear Algebra class, because the textbook often does and I don't want to introduce unnecessary confusion; but usually in my own work, and sometimes when I teach upper-level math classes, I use 0-based indexing when it's necessary to choose.

Re: Why do arrays start at 0?

#569

Post by dboreham » Thu, Aug 25, 2022, 3:00 AM UTC

dahart wrote: post #503

dboreham wrote: post #434

Earlier quoted context omitted.

"just subtract one" would take a long time 50-60 years ago.

Integer add/subtract never really took a long time. Slower than today’s sub-nanosecond, and it depends on the computer, but there were CPUs in the mid 1960s doing millions of instructions per second. They weren’t crazy slow, they were just crazy expensive.

A million, perhaps. But you're talking about adding one instruction to every single data access. Plus your code bloats up with all those extra dec instructions. BCPL and C were created for departmental and lab computers like the pdp-9.

Note, for example that the mighty 6502 succeeded in the market because its designers had heard from customers that the $100 price for the 6800 was too much, so they removed some instructions and addressing modes to get the die small enough that it could be sold for $20.

Re: Why do arrays start at 0?

#570

Post by chii » Thu, Aug 25, 2022, 3:00 AM UTC

kergonath wrote: post #409

kccqzy wrote: post #376

Earlier quoted context omitted.

I must say in this case Google does it right: https://cloud.google.com/spanner/docs/reference/standard-sql... In Google standard SQL, to access an array it is simply not allowed to put a number inside square brackets. You must specify which way you mean. So `SELECT some_numbers[OFFSET(1)], some_numbers[ORDINAL(1)]` is allowed but not `SELECT some_numbers[1]`.

That sounds actually great to avoid any ambiguity. At the cost of a bit of verbosity, though.

that's actually good verbosity, because the intent is very clear using this method, and multiple people can read the code and unambiguously identify the intent without having to talk to the original author.

This type of verbosity makes sense in a big organization where the left hand doesn't talk much to the right hand much, so communication naturally evolves to happen at the code level.