Global variable wrapped in a function

I'm learning Julia as part of my PhD in economics but I've come across an issue that doesn't make sense to me. I'm trying to write a function that performs some preliminary calculations then conducts a while loop and returns some value. I want to do this without using global variables. For some reason I can't get it to work. See the minimal working example below which returns a undefined variable error for z.

function test_me(n)
x = 2 + 1
y = x - 1 
i = y
while i <= n 
    println(i)
    i += 1
    z = 3*i
end 
return z 
end

I can solve the problem easily by making z a global variable.

function test_me2(n)
x = 2 + 1
y = x - 1 
i = y
while i <= n 
    println(i)
    i += 1
    global z = 3*i
end 
return z 
end

I'm confused as I was under the impression that by wrapping the while loop in a function implies that z is in the local scope and the global declaration is unnecessary. For example the code below works as expected.

function test_me3(n)
i = 1
while i <= n 
    println(i)
    i += 1
    z = 3*i
end 
return z 
end

I apologise if this issue is trivial. Any help is really appreciated. Thanks.

Solution

Just put a local z or alternatively a z = 0 before your while loop such that z is defined in the loop.

For more on this check out the scoping page of the Julia documentation and the local keyword docstring.