There are just two cases to be concerned about: 1/ $var is local to the loop, 2/ $var is global to the loop.

1/ If $var is local to the loop the desired behaviour is that you get a fresh version of $var each time through the loop. In that case use a my declaration where the first value is assigned to $var within the loop.

2/ If you want $var to retain some previous value from one iteration of the loop to the next (maybe you are looking for a largest value or something) then $var should be global to the loop. In that case use a my declaration just before the loop and assign an appropriate initial value if required.