Julia Variable scope

Question

I\'m trying to use some global variables (m, n, r) in a while loop, but julia 1.0.0 is telling me that those variables aren\'t defined. The code works with julia 0.7.0, with som

Answer 1

You have to declare variables you define in global scope and assign to in loop local scope as global inside the loop like this:

m = readline()
n = readline()
m = parse(Int, m)
n = parse(Int, n)
r = m % n
while (r > 0)
        println( "m: $(m) n: $(n) r: $(r)" )
        global r = m % n
        global m = n
        global n = r
end

The reason you have to do it is that while loops introduce a new local scope, so without global keyword assignment like m = n tells Julia that m is a local variable inside a while loop so then in the line println( "m: $(m) n: $(n) r: $(r)" ) Julia decides that m is yet undefined.

See also https://docs.julialang.org/en/latest/manual/variables-and-scoping/ and Why does this assignment inside a loop fail in Julia 0.7 and 1.0? for further explanation of the scoping rules in Julia.