i is for index. j is simply the next letter and we're too lazy to think up something meaningful

A useful tip I picked up was to use ii instead of j for an inner loop. It's far more distinct than j.

If for some terrible reason you have even more inner loops you can easily continue the trend i, ii, iii, iiii, iiiii - or iv, v if you're feeling roman

It depends. x and y are either elements or coordinates, a and b usually elements though in e.g. Haskell reserved (by convention) for type variables.

The i j k l series is reserved for indices. n m etc. are the counts of something, as such you'll see i counting up to n. Both are due to mathematical sum notation and general mathematical convention. Random google result:

Let x~1~, x~2~, x~3~, …x~n~ denote a set of n numbers. x~1~ is the first number in the set. x~i~ represents the ith number in the set.

...if you're using a language in which you use i often chances are you should stop coding in C and get yourself a language with iterators. Manual loops are a bug magnet.

x is used for map, filter, etc. a and b are used for sorts, comparisons and merges. y might be used if I'm doing multiple lambda expressions (but that means I'm in a bad place already). I have no idea why, but these are firm rules in my brain.

People who name iterators with one letter have no soul.

I generally use a for each type loop or a map because I am usually applying some function across a collection, and in both cases I use the singular name from the collections plural.

’Cities.map(city -> …)’

For (val city in cities)

If I actually need the index for some reason I still prefer loop structures that give me the index and the item together

*note syntax pulled out of my head and not necessarily belonging to any specific language.

For ( city, index in cities)

cities.map((city, index) -> … )

If I need to double loop a matrix array I would use rowIndex and ColIndex for the indexes.

I find it hard to read when these are together:

• i, j, l
• n, m, u, v, w

From all the possible character combinations, somehow the lookalike combinations are among the most popular. Yes, probably comes from math. I hated it even more when my math prof's i and j on the board were indistinguishable.

It's my understanding that i,j are conventionally used in mathematics which carried over into programming, but specifically it comes from Fortran in which all integer variables start with "I" through "N" based on said mathematical convention

for <thing> in <amount> do...

I don't like i and j since they are commonly used for imaginary numbers. I like to start on n. Probably because I do DSP.

WTF, I have never used nor seen "j."

I don't usually have to name these variables these days though. Pretty much everything I use has foreach or some functional programming type stuff.

And like that, the off-by-one mistakes disappear.

chuckles in Python

don't mind i but personally always use index or x, y, z for games

Well. I guess I'm then a some kind of heretic then. 🤷

I started using the first letter of the thing I am iterating over. This is particularly helpful with nested loops so I can easily remember which index variable corresponds to which thing.

When my brain doesn’t work I’ll resort to naming them the single of the plural. Like keys turns into key when i don’t wanna call it “objkey” or “outrageouslylongnamethatmayormaynotbeafittongwordtodescribeakey”