# Declaration of variables
**URL:** https://discourse.julialang.org/t/declaration-of-variables/103508
**Category:** General Usage
**Tags:** question
**Created:** [September 4, 2023, 1:23pm UTC](https://discourse.julialang.org/t/declaration-of-variables/103508 "2023-09-04T13:23:39Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Alois](https://discourse.julialang.org/u/Alois)
#### Post date: [September 4, 2023, 1:23pm UTC](https://discourse.julialang.org/t/declaration-of-variables/103508/1 "2023-09-04T13:23:39Z")
How is a variable declared as a simple Float64, say, without initializing it?
Something like `A= Array{Float64, 0}(undef)`, which works for vectors.
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [September 4, 2023, 1:29pm UTC](https://discourse.julialang.org/t/declaration-of-variables/103508/2 "2023-09-04T13:29:17Z")
You don´t . A `Float64` is an immutable value, meaning that there is nothing that is its “existence” except its value. What you can is define its scope without giving it a value:
```julia
function f()
local a
for i in 1:3
if i == 1
a = 1
end
a = a + 1
end
return a
end
```
(the function above errors if you remove `local a` because then a is not initialized in the second iteration of the loop, as the scope of `a` would be limited to the first iteration).
ps: You could there also use `local a::Float64` to specify the type of `a`).
---
### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [September 4, 2023, 1:42pm UTC](https://discourse.julialang.org/t/declaration-of-variables/103508/3 "2023-09-04T13:42:00Z")
To nitpick I think `isbits` is a better abstraction than `isimmutable` here. Regardless a `Float64` is represented by exactly eight bytes, and all those 2^64 possible values correspond to a double precision number, so there’s no space to encode the state of not being initialized.