# UndefVarError on loop iterator in while loop

**URL:** <https://discourse.julialang.org/t/undefvarerror-on-loop-iterator-in-while-loop/14747>\
**Category:** General Usage\
**Created:** [September 10, 2018, 2:46am UTC](https://discourse.julialang.org/t/undefvarerror-on-loop-iterator-in-while-loop/14747 "2018-09-10T02:46:09Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Joseph\_Fletcher](https://avatars.discourse-cdn.com/v4/letter/j/f19dbf/32.png) [@Joseph\_Fletcher](https://discourse.julialang.org/u/Joseph_Fletcher)\
**Post date:** [September 10, 2018, 2:46am UTC](https://discourse.julialang.org/t/undefvarerror-on-loop-iterator-in-while-loop/14747/1 "2018-09-10T02:46:09Z")

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When I try to run this code I copied from a tutorial, I get an error.

```julia
t = 0
while t<5
    println(t)
    t+=1 # t = t + 1
end

```

`LoadError: UndefVarError: n not defined`  
Did I do something wrong while setting up Julia?

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<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [September 10, 2018, 3:18am UTC](https://discourse.julialang.org/t/undefvarerror-on-loop-iterator-in-while-loop/14747/2 "2018-09-10T03:18:52Z")

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In short, in global scope, you would need `global t += 1` instead since you are modifying a global variable. In a function, your code would work as is.

See [https://github.com/JuliaLang/julia/issues/28789](https://github.com/JuliaLang/julia/issues/28789) for some discussion about this.

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<div class="post-metadata">

**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [September 10, 2018, 6:19am UTC](https://discourse.julialang.org/t/undefvarerror-on-loop-iterator-in-while-loop/14747/3 "2018-09-10T06:19:38Z")

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> [@Joseph\_Fletcher](#):
>
> from a tutorial

Which one? Might be a good idea to update this for Julia v1.0.

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<div class="post-metadata">

**Author:** ![nuktalop](https://avatars.discourse-cdn.com/v4/letter/n/3ec8ea/32.png) [@nuktalop](https://discourse.julialang.org/u/nuktalop)\
**Post date:** [November 3, 2018, 1:28pm UTC](https://discourse.julialang.org/t/undefvarerror-on-loop-iterator-in-while-loop/14747/4 "2018-11-03T13:28:42Z")

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I got the same issue. This code can be found here: [JuliaTutorials/04. Loops.ipynb at main · JuliaAcademy/JuliaTutorials · GitHub](https://github.com/JuliaComputing/JuliaBoxTutorials/blob/master/introductory-tutorials/intro-to-julia/04.%20Loops.ipynb)  
andin the youtube tutorial: [A Gentle Introduction to Julia - YouTube](https://www.youtube.com/watch?v=4igzy3bGVkQ)