CODEWITHSUNDEEP
actionscript-3flash
popClingwrap
popClingwrap

Reputation: 4217

Why does uint break my for loop?

This is not really a problem as the fix is simple and pretty costless. I'm guessing it's some property of for or uint that I don't understand and I just would like to know what is going on so...

Using ActionScript 3 I set up a for loop to run backwards through the elements of a Vector.

var limit:uint = myVector.length-1;
for(var a:uint = limit; a >= 0; a--)
{
    trace(a);
}

When I run this it outputs 2, 1, 0 as expected but then moves on to 4294967295 and begins counting down from there until the loop times out and throws an Error #1502.

The fix is simply to type a as int rather than uint but I don't get why. Surely I am dealing with values of 0 and greater so uint is the correct data type right?

I guess that 4294967295 is the max value for uint but how does my count get there?

If you do

var myUint:uint = 0;
trace(myUint - 1);

Then the output is -1 so why, in my loop should I suddenly jump back up to 4294967295?

Sorry for the slightly rambling question and cheers for any help.

Upvotes: 1

Views: 174

Answers (3)

WeslomPo
WeslomPo

Reputation: 11

In binary - first BIT of number is minus, that is in int values. In UINT value that is just a BIT of value. One byte int looks like 1000 0000 == -127 and 0111 1111 = 127 One byte uint looks like 1000 0000 == 128 and 0111 1111 = 128

This is it.

Upvotes: 1

pedro_sland
pedro_sland

Reputation: 5705

You are close. As you said, your loop gives you 2, 1, 0, 4294967295. This is because uint can't be negative. Your loop will always run while a >= 0 and since it is never -1 to break the loop condition, it continues to loop forever.

var myUint:uint = 0;
trace(myUint - 1);

I didn't test this but what is probably happening is that myUint is being converted to an int and then having 1 subtracted. The following code should be able to confirm this.

var myUint:uint = 0;
trace((myUint - 1) is uint);
trace((myUint - 1) is int);

To fix your loop you could use int or you could use a for each(var x:Type in myVector) loop if you don't need the index (a).

Upvotes: 4

Charles HETIER
Charles HETIER

Reputation: 2094

an iteration and a a-- will occur when a is 0, thus as your int is not signed, the max value for this type will be set -> this is the way minus values are set in unsigned types.

Change your code into:

var limit:uint = myVector.length-1;
for(var a:uint = limit; a > 0; a--)
{
    trace(a);
}

Upvotes: 3

Related Questions