UndefVarError but variable is clearly defined - julia

Question

Suppose I have the following code which has two nested while loops.
struct Parameters
maxIter1::Float64
maxIter2::Float64
tolerance1::Float64
tolerance2::Float64
end
mutable struct Guess
x1::Float64
x2::Float64
end
function solveModel(par::Parameters,initGuess::Guess)
iterate1 = 0
error1 = 0
guess = initGuess
while (par.iterate1 < par.maxIter1 && error1 > par.tolerance1)
iterate1 += 1
iterate2 = 0
error2 = 0
guess.x2 = initGuess.x2
while (iterate2 < par.maxIter2 && error2 > par.tolerance2)
iterate2 += 1
z2 = solveInnerProblem(par,guess)
newGuess = update2(par,guess,z2)
error2 = computeError2(newGuess,guess)
guess = newGuess
end
guess = newGuess
end
end
I get an error message,
Note: the reference to the line number is erroenous - line 294 of my code contains no mention whatsoever of newGuess.
The error message goes away if I comment out the line
guess = newGuess
In the outer loop (last line before the final two end lines in the code snippet). I'm quite confused as to why this is happening. The variable newGuess is clearly defined, but Julia says it is not defined...

Answer 1

newGuess is a local variable, which means that it is defined in a localized part of the program rather than all the program. In the case of a local variable defined within a loop like a while statement, the variable is undefined outside the while loop within which it is defined, which is the inner while loop of your function. So the "not defined" error is because the program is trying to access the variable outside of its local scope-- it was defined before, but not when the error occurs.
You may need to define newGuess higher up, within the function, but before the inner while statement.