Thread: i j k variable names

  1. #1
    Its hard... But im here swgh's Avatar
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    Apr 2005

    i j k variable names

    Am I correct in the face programmers use I J and K as variable names for for loops since the FORTRAN language? Was the language designed to accept only these variables?

  2. #2
    The superhaterodyne twomers's Avatar
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    Dec 2005
    I use i, j, k out of habit, and always assumed i stood for iterator or something and that j and k followed suit alphabetically. I don't know about the fortran link ... but I couldn't see any language accepting only three variables!

  3. #3
    Registered User
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    Aug 2006
    If the variables are loop specific, then I use i,h,j, and k mostly. i is just for interger/iterator really, the others are just near it in the alphabet.

  4. #4
    Crazy Fool Perspective's Avatar
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    Jan 2003
    Check any math book/paper, you'll see i, j, and k are pseudo standards for indices on summations, integrals, etc... I'm pretty sure math predates computers.

  5. #5
    pwns nooblars
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    Oct 2005
    Portland, Or
    I am with Perspective, it has been in math for a lot longer than computers have been around.

    One reason you see a lot of it though, is habbit, some programmers who are newer, or even ones that have been doing it for a while, learned to use i in loops, and if you have nested loops j, k, and so on.

    I don't even think about it anymore, when I go to do a for loop or while loop

    for(int i = 0; i < value; i++) {
      int j = 0;
      while(j < 100) { 
        /*stuff that changes j in more/less than +1 per loop */ 

  6. #6
    Registered User
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    Sep 2006
    New York, New York
    I've never even heard of people using i, j and k as variables for anything. I'm used to seeing variable names like count or x for loops.

  7. #7
    The Right Honourable psychopath's Avatar
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    Mar 2004
    Where circles begin.
    I've seen names like 'idx' or 'iter' used occasionally, but usually i, j, k, etc.
    M.Eng Computer Engineering Candidate
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    Robotics and graphics enthusiast.

  8. #8
    Join Date
    Feb 2002
    I use i, j, k on the first pass. After that, I'll substitute a more meaningful name so that I don't have to wonder why I've got i+j*60 somewhere in my code.
    If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein

  9. #9
    Cat without Hat CornedBee's Avatar
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    Apr 2003
    Agree with those that say it comes from mathematics, and want to add that 'i' derives from index, not integer or iterator.
    All the buzzt!

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  10. #10
    (?<!re)tired Mario F.'s Avatar
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    May 2006
    I use i, j, k for iterations or simple short lived flag-like variables when it makes sense. To me. Which probably not always makes sense to others. I'm also known to use n and m. Usually when I want to convey limits on dimensions or sizes
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  11. #11
    Registered User Rennor's Avatar
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    Aug 2006
    As a beginner I used to use x mostly and then y and z. When starting to write some 2D gfx effects those quickly changed to i, j and k since x,y and z are for coordinates

    Then the mixture was complete, sometimes i, j and k were just for looping, sometimes they represented "temporary" variables where x = i, y = j and z = k.

    Go figure.

    Nowadays I use only i when I try out something quickly, if I need more variables they usually come out with proper names. Being professional and responsible for quality makes me automatically name everything and comment them properly according to our styleguides

  12. #12
    Registered User
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    Oct 2001
    Quote Originally Posted by swgh
    Am I correct in the face programmers use I J and K as variable names for for loops since the FORTRAN language? Was the language designed to accept only these variables?
    By my thinking, you are correct. In FORTRAN, variables that begin with the letters I thru N are by default of type INTEGER. Variables that begin with any other letter are by default REALs. So you can see how this would have led to using I, J, and K for for-loop indices.

  13. #13
    Reverse Engineer maxorator's Avatar
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    Aug 2005
    I usually use I, N and E. I don't know why.
    "The Internet treats censorship as damage and routes around it." - John Gilmore

  14. #14
    Frequently Quite Prolix dwks's Avatar
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    Apr 2005
    I use x, y, and z (and a, b, c etc if required). If I need to use coordinates, I use xp, yp, etc (for X-position, Y-position). I don't know why, either.

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