This is a compromise between being technically correct and just doing it. This creates a local scope for you to work in.
let A = 5
for i in 1:10
A = A+i;
end
println(A)
# Do other stuff that uses A
end
If you really want want the minimum fix, you can add a global declaration in the loop. I do not recommend it.
A = 5
for i in 1:10
global A = A + 1
end