For-loop variable scope confusion

Question

I have noticed a weird behavior of the variables in for loops. It's not really a problem, but it disturbs me a lot.
Actually I've created two loops this way:

for (var i:uint; i<19; i++) SomeFunction (i);
for (var i:uint; i<26; i++) SomeOtherFunction (i);

What I received was a compilation warning:
Warning: Duplicate variable definition.

This warning really surprised me. Nothing like that ever happened to me in other languages.
It seems that the i variable gets into the scope that is higher in the hierarchy and becomes available out of the loop's block. I've also tried to embrace the loop block in a curly brace, but it didn't change anything.
Why does it happen? Is it normal? Is it possible to avoid it? For now I've just set different names for both of the variables, but that's not a real solution I think. I'd really like to use the i-named variable in most of my for-loops.

Answer 1

yes, the loop increment variable is in the scope of the loops parent, not inside the loop itself. This is intentional, for examples like this:

public function getPositionOfValue ( value:String ) : int
{
    for ( var i:int = 0; i < someArray; i++ )
    {
        if (someArray[i] == value )
        {
            break;
        }
    }

    return i;
}

this allows you to access the value of i once the loop is over. There are lots of cases where this is very useful.

What you should do in the cases where you have multiple loops inside the same scope is var the i outside of the loops:

public function getPositionOfValue ( value:String ) : int
{
    var i:int;

    for ( i = 0; i < 15; i++ )
    {
        //do something
    }

    for ( i = 0; i < 29; i++ )
    {
        //do something else
    }

    return i;
}

then you get rid of your warning. The other thing to consider is to name your loop increment variables something more descriptive.

Update: Two other things to consider:

1) you shouldn't use uints except for things like colors and places where Flex expects a uint. They are slower than int's to use. Source]1 Update: it looks like this may no longer be the case in newer versions of the flash player: source

2) when you var a loop increment variable inside of a loop declaration, you want to make sure you set it to the proper initialization value, usually 0. You can get some hard to track down bugs if you dont.