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Why do arrays start at 0?

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Re: Why do arrays start at 0?

#321

Post by steadicat »

zajio1am wrote: post #80
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…

> 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. It is more like counting from 1 is just a leftover from times where zero was not commonly considered as number. Once one have zero, it makes sense to use it as an initial ordinal (see e.g. set theory, where zero is both initial ordinal and initial cardinal number, way before com…

When talking about discrete things, 0 has a specific meaning: it is the absence of things. It does not make sense to count the 'first' element as the 0th. When you encounter the 'first' element, how many elements do you have? 1.

This is of course different for continuous quantities. When counting seconds, for example, we should absolutely start from 0.

Re: Why do arrays start at 0?

#322

Post by [deleted] »

diego_sandoval wrote: post #273

Because otherwise you would be wasting a perfectly good number for no reason, which means you need to use more bits to do the same thing. To write 4 numbers (including zero) you only need two bits 0: 00 1: 01 2: 10 3: 11 To write 4 numbers if you avoid using the number zero, you need three bits 1: 001 2: 010 3: 011 4: 100 If you extrapolate that a little bit, you'll realize that you'll need two bytes (1 Byte + 1 bit…

[deleted]

Re: Why do arrays start at 0?

#323

Post by vukgr »

saalweachter wrote: post #318
jiveturkey wrote: post #312

Earlier quoted context omitted.

> additional computational overhead at compile time, not runtime.

For constant addressing; for arr[i] = 2, you'll still need to subtract 1 from i with 1-based addressing when converting to machine instructions.

Can't say I've really thought this through, but couldn't you just subtract 1 (*sizeof(X)) from the arr address?

Re: Why do arrays start at 0?

#324

Post by just_boost_it »

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.

We're 20 years past the point where you can expect everyone in tech to trace every instruction down to machine instructions. Higher level languages abstract away the need for it, and for the most part, we can rely on the authors of those languages to make many of the decisions that impact performance. The rest of us learn about these details on posts like this. It's not a sad fact, in fact it's probably one of the most useful things that's happened in tech. It frees people to think about other problems.

Re: Why do arrays start at 0?

#325

Post by anigbrowl »

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.

No. Your age is 1-indexed. It's a 'birthday' in English and German ('geburstag'); in French it's 'anniversaire', and so on. But pretty much everyone indexes age from 1. The fact of your birth is the transition from (legal) non-existence to existence, the equivalent of a dimensionless point.

Re: Why do arrays start at 0?

#326

Post by wizofaus »

msk-lywenn wrote: post #282
411111111111111 wrote: post #277

Earlier quoted context omitted.

Uh I'm confused but don't know c++. why doesn't that loop end instantly? I mean length - 1 Or does it only terminate when the number underflows? Terribly confused here

It’s a condition to run, not a condition to stop

That was my reaction - why should anyone think it might be the latter? Are there languages that do have such a syntax without explicit keywords ("do...until")?

Re: Why do arrays start at 0?

#327

Post by blueflow »

Blikkentrekker wrote: post #313
blueflow wrote: post #269

Earlier quoted context omitted.

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.

“machine code” isn't really the zero point that's special nowadays. The code the programmer wrote is compiled to something such as LLVM IR, LLVM IR is further compiled by LLVM to Assembly, this is further compiled by an assembler into machine code, and then the c.p.u. further compiles this to it's internal code as it executes it. “machine code” really is no more special in this chain of events than, say, LLVM IR.

Machine code is special because its the only thing the CPU can actually execute.

Re: Why do arrays start at 0?

#329

Post by unbalancedevh »

goatlover wrote: post #136
themacks wrote: post #49

Earlier quoted context omitted.

Typical counting of things starts from 0. If you count apples you implicitly start at zero and add 1 for each apple. If you count age, you start at birth (0) and count years; one for each birthday. That isn't zero based. The difference is the index of the item between the starting point and the next item. In zero based this item is number 0, in one based, this item is number 1. The first year of life is generally con…

> If you count apples you implicitly start at zero and add 1 for each apple. If that's the case, then how did the ancient Greeks or Romans count before zero was an acceptable concept in their counting system?

By describing it in other ways, I imagine: "How many apples do you have?" "I don't have any."

Re: Why do arrays start at 0?

#330

Post by Koshkin »

The first element having the index zero may be natural or unnatural depending on the context. In mathematics, we count the rows in a matrix starting from 1, but we count the monomials in a polynomial starting (or ending) with 0. Generally, there is less need to use zero as the starting index: the Common Era does not have "the year zero" (there, -1 is followed by +1), etc.
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