# Using structs in for loops?
**URL:** https://discourse.julialang.org/t/using-structs-in-for-loops/25998
**Category:** New to Julia
**Created:** [July 3, 2019, 10:47pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998 "2019-07-03T22:47:59Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)
#### Post date: [July 3, 2019, 10:47pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/1 "2019-07-03T22:47:59Z")
Hey guys
Can anyone explain to me why k is not defined in this case?
```julia
struct MyStruct
id::Int
x::Float64
y::Float64
end
function SquareGrid(nStart,nEnd,nStep)
x = collect(range(nStart,nEnd, step=nStep))
nP = size(x)[1]
for i = 1:nP
k = MyStruct(i,x[i],x[i])
println(k)
end
return k
end
```
It gives me the error:
```julia
ERROR: UndefVarError: k not defined
Stacktrace:
[1] SquareGrid(::Int64, ::Int64, ::Float64) at C:\Users\Ahmed Salih\OneDrive - Aarhus universitet\AU-CIVIL1\2\ThermoSim\Grid.jl:32
[2] top-level scope at none:0
```
Did they change something with scope again? Using Julia 1.1.1
Kind regards
---
### Author:  [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)
#### Post date: [July 3, 2019, 10:54pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/2 "2019-07-03T22:54:28Z")
Figured it out, I just had to write “global” infront of k in the for loop. Maybe there is a better way? My approach is not working so well right now, since I want “k” ie. my struct to hold x and y location for many nodes of different id’s - just can’t figure out how to achieve that
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [July 3, 2019, 11:03pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/3 "2019-07-03T23:03:39Z")
You can write `local k` in front of the loop.
---
### Author:  [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)
#### Post date: [July 3, 2019, 11:29pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/4 "2019-07-03T23:29:03Z")
> [@kristoffer.carlsson](#):
>
> locak
Thanks! That worked
---
### Author:  [@jlperla](https://discourse.julialang.org/u/jlperla)
#### Post date: [July 4, 2019, 2:24am UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/5 "2019-07-04T02:24:22Z")
> [@Ahmed\_Salih](#):
>
> I just had to write “global” infront of k in the for loop.
You want to avoid `global` like the plague… Unless it is a very deliberate design decision, which is rarely necessary outside of packages
---
### Author:  [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)
#### Post date: [July 4, 2019, 1:51pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/6 "2019-07-04T13:51:22Z")
I am trying to generate a grid of nodes (ie. a grid of points) and I want each point to be described by the “MyStruct”, so that in the future I can access the values of this node using MyStruct (via the id field name) - I don’t know if this is the best approach but what I am doing currently is not working since MyStruct is only able to handle one point at a time… Any suggestions?
Kind regards
---
### Author:  [@jlperla](https://discourse.julialang.org/u/jlperla)
#### Post date: [July 4, 2019, 4:04pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/7 "2019-07-04T16:04:13Z")
My suggestion is to avoid defining custom structures until you get a little more comfortable with the language. Unless you the structures for multiple dispatch, having it return matrices of the `id,x,y` (which you can collect in a named tuple if you wish to have them in one place) may be easier.
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [July 4, 2019, 4:31pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/8 "2019-07-04T16:31:13Z")
> [@jlperla](#):
>
> My suggestion is to avoid defining custom structures until you get a little more comfortable with the language.
Using structs is pretty much the first thing you learn about the language after some basic syntax.
> [@Ahmed\_Salih](#):
>
> I don’t know if this is the best approach but what I am doing currently is not working since MyStruct is only able to handle one point at a time… Any suggestions?
One suggestion would be to have an array of `MyStruct` so something like
```julia
struct MyStruct
id::Int
x::Float64
y::Float64
end
function SquareGrid(nStart,nEnd,nStep)
x = collect(range(nStart,nEnd, step=nStep))
nP = size(x)[1]
return [MyStruct(i, x[i], x[i]) for i in 1:nP]
end
```
and then you get
```julia
julia> ks = SquareGrid(1, 10, 1)
10-element Array{MyStruct,1}:
MyStruct(1, 1.0, 1.0)
MyStruct(2, 2.0, 2.0)
MyStruct(3, 3.0, 3.0)
MyStruct(4, 4.0, 4.0)
MyStruct(5, 5.0, 5.0)
MyStruct(6, 6.0, 6.0)
MyStruct(7, 7.0, 7.0)
MyStruct(8, 8.0, 8.0)
MyStruct(9, 9.0, 9.0)
MyStruct(10, 10.0, 10.0)
julia> ks[3].id
3
```
---
### Author:  [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)
#### Post date: [July 4, 2019, 9:48pm UTC](https://discourse.julialang.org/t/using-structs-in-for-loops/25998/9 "2019-07-04T21:48:03Z")
Thanks exactly what I wanted, and thank you for showcasing how to access the individual elements. If someone wants to extract the whole array I discovered this notation:
```julia
ks.↦ :id
```
Taken from this answer [Best way to access field in array of structs in Julia - Stack Overflow](https://stackoverflow.com/questions/46820304/best-way-to-access-field-in-array-of-structs-in-julia)