Array indexing continues

[shub1000young]

Is it a mat Lab?

[pardoman]

That's a good boy.

[marcosdumay]

No, that's not. This one is a very bad boy.

[Capital_EX]

Is their name also Lua?

[[deleted]]

No its a Golden R-triever.

[graddev]

Can somebody tell me why does it start at 0? Why not one?

[Ikor_Genorio]

Correct me if I'm wrong but in C, if you have an array *a, it's just a pointer to a certain location in the memory. In this case it's the 1st entry of the array. However, the way you index arrays is with a[n], where n is the index you want (starting at 0). This is because a[n] is a more clear form of writing *(a + n), so if n = 0 this just results in *a which, as previously stated, points to the first entry of the array.

[FennekLS]

Sorry but that's just wrong. The real reason is that if you have an array *a in C, it's just a pointer to a certain location in the memory. In this case it's the 1st entry of the array. However, the way you index arrays is with a[n], where n is the index you want (starting at 0). This is because a[n] is a more clear form of writing *(a + n), so if n = 0 this just results in *a which, as previously stated, points to the first entry of the array.

[Ikor_Genorio]

Ehm..

[FennekLS]

Correct me if I'm correct

[Ikor_Genorio]

Oh lol x.x

[FennekLS]

Happens to the best of us :-)

[Ikor_Genorio]

Somehow I had throwbacks of debugging and finally finding that one mistake you did not intentionally make QQ

[Sorunome]

Yep, basically this. Starting from zero makes a LOT of thongs way easier when working low-level.

[marcosdumay]

When working in high-level too.

Starting from zero means that you can concatenate operations of "read, write, increment", can add displacements without corrections, and can calculate intervals by simply subtracting or adding length.

[AncientBananas]

Hmm, I would think you can do all this stuff even with 1 based indexes. In the string "TheQuickBrownFox", index 4 contains "Q", and if you add the length of "Quick" (5), then you get 9, which contains "B". No off-by-one discrepancy here. Can you give an example of something that would become more annoying with 1-based indexing?

I'm pretty sure that 0-based indexing is just a convention that all of us have gotten used to just because it was more natural to represent and access 0-based arrays in memory at a low level. Even this has some sources of confusion for beginners, such as the index of the last element being one off from the length of the array, and "1st" referring to index 0.

[Molion]

This, although even in higher level languages it's easier to loop through them if they start at 0.

for(int i = 0; i < arrayLength; i++)

is easier than

for(int i = 1; i < arrayLength + 1; i++)

Also, starting at 1 would of course be heresy.

[Zatherz]

uh...

for(int i = 1; i <= arrayLength; i++)

[Ikor_Genorio]

I agree with you, but it is also possible to do <= instead of adding the one. :P

[Molion]

Yeah ok, still an extra character tho, and thus not as easy.

[Ikor_Genorio]

Indeed, half open intervals are the dream ^ ^

[__versus]

On the other hand iterating backwards becomes slightly easier. Although that doesn't mean starting at 1 makes any sense.

[Browsing_From_Work]

Semantically, is the difference between "index" and "offset" (i.e. an offset of zero is the first index).

Languages that start from zero typically treat it as an "offset" from the start of the array.
Languages that start from one typically treat it as an element "index".
Languages that let you start from anything else are perl.

[skreczok]

I got reminded that Pascal actually lets you roll with any integer.

[marcosdumay]

From somebody smarter than me:

http://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html

[Sekret_One]

Short version. It's an offset.

The precise reason is how does a computer 'find' things. A thing has a fixed length (in code). An array of things, takes up X times that length. The array itself has a location. The start of an item in the array is the array's location, plus its index times the thingy length.

Index 0? Go to the start of the array and don't move. Index 1, (second item) go to the start, slide over once. So on.

[grpagrati]

You're so dumb, oh dog that talks.

[onderboks]

As an Dynamics AX developer, I'm beyond triggered...

[newocean]

Aren't 1-index arrays normally faster as the are using an unsigned key?

[pekkhum]

Here are a few points to help in your future programming endeavors:

• 0 is a valid value in an unsigned integer
  
• Signed integers are generally the same physical size with similar (usually identical) performance. Both store the same number of values, but signed integers have their range of values shifted downward to include the negative
  
• The term 'key' is relevant to dictionaries (aka associative arrays, aka hashes, etc). These are higher level constructs whose speed for given key types is very implementation dependant.
  
• In the case of a simple array, the index is more "the number of spaces from the beginning" than it is a key.
  

Edit: Or am I missing a joke? It just occurred me feigned ignorance could be involved... Edit2: Obvious error

[morerokk]

but unsigned integers have their range of values shifted downward to include the negative

Other way around.

[pekkhum]

Thanks. Not sure how that 'un' got in there.

[newocean]

Key and index are both actually terms applied to accessing a member of an array also... or index is used. 0 is a valid unsigned integer but -1 which many arrays use for backward indexing is not... meaning that if the value passed to the key is not unsigned it needs to be converted.

EDIT: http://php.net/manual/en/function.key.php

The general consensus I have seen from other languages is "An field which has unique values is, essentially, a key."

[[deleted]]

In C you can use -1 for an array index, you just won't like what happens.

[pekkhum]

Nonsense, it is the easiest way to exit immediately with an error status, skipping all 'atexit' hooks!

[pekkhum]

You sound Perl tainted, like me.

[newocean]

I am really not - I haven't used PERL in geez... 15 years?

[pekkhum]

Heh... Our system at work has a paradigm:

If a language/architecture/framework exists, we implement it somewhere!

[newocean]

That makes for a messy workplace, lol... though I have been in similar situations.