# Global variable disappears
**URL:** https://discourse.julialang.org/t/global-variable-disappears/4021
**Category:** General Usage
**Tags:** scope
**Created:** [May 31, 2017, 7:03pm UTC](https://discourse.julialang.org/t/global-variable-disappears/4021 "2017-05-31T19:03:19Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@ulysses](https://discourse.julialang.org/u/ulysses)
#### Post date: [May 31, 2017, 7:03pm UTC](https://discourse.julialang.org/t/global-variable-disappears/4021/1 "2017-05-31T19:03:19Z")
I have the following scenario for initialization of a global variable which fails for some mysterious reason.
```julia
// t.jl
n = 1
function f()
if n == 1
n = 2
end
println(n)
end
...
julia> include("t.jl")
f (generic function with 1 method)
julia> f()
ERROR: UndefVarError: n not defined
Stacktrace:
[1] f() at t.jl:3
```
While it is perfectly clear to, e.g., just print a global variable:
```julia
// t.jl
n = 1
function f()
println(n)
end
...
julia> include("t.jl")
f (generic function with 1 method)
julia> f()
1
```
Can anyone explain the reason which causes global variable disappear? What are the limitations on using global variables?
---
### Author:  [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)
#### Post date: [May 31, 2017, 7:08pm UTC](https://discourse.julialang.org/t/global-variable-disappears/4021/2 "2017-05-31T19:08:54Z")
In order to assign global variables from a function one must use the keyword `global`.
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [May 31, 2017, 7:09pm UTC](https://discourse.julialang.org/t/global-variable-disappears/4021/3 "2017-05-31T19:09:02Z")
A variable is either global or local within a given scope, never both. By having an assignment `n = 2` inside your first function, Julia treats `n` as a new local variable everywhere inside the function, and that variable is undefined until the `n = 2` line.
If you want to set a global variable, you need to explicitly mark it as global to prevent this from happening:
```julia
julia> n = 1
1
julia> function f()
global n
if n == 1
n = 2
end
println(n)
end
f (generic function with 1 method)
julia> f()
2
julia> n
2
```