You really should make friends with use strict and its cousin use warnings... With the code as given:

• use strict complains about $i, which is used in the loop, but doesn't seem to be declared anywhere

  -- that's what it means by 'Global symbol "$i" requires explicit package name'... we just have to accept that when looked at from the correct angle, this makes perfect sense.

• use warnings would warn you that each time $i is used it is uninitialised (though with use strict you wouldn't get that far !).</c>