Declaring a variable of a class

Question

Hi,
I'm creating a stack to save math operations that have occurred so that I can use an undo button to remove those operations.  I followed this implementation:
http://deviltechie.wordpress.com/2010/10/03/create-a-stack-queue-data-structure-in-flex-ac tionscript/#comment-71
I created two actionscript class files Node.as and Stack.as like what was done in the link but I do not know how to create a variable of that class in the Script area of my .mxml file.  My code looks like this:
    <fx:Script>
        <![CDATA[
            import dataStore.Node;
            import Stack;
            var storage:dataStore.Stack;
        ]]>
    </fx:Script>
I was trying to create a variable called storage of type Stack but I get an error saying "1046: Type was not found or was not a compile-time constant: Stack."
Any information on how to correctly create a variable of a stack class in the Script of my main MXML file would be very helpful.
Thanks

Answer 1

Thanks spoboyle and pauland,
By adding a new package called dataStore I was able to create a variable of Stack so you two will get the answer and helpful answer to my question. 
Currently I am getting a error when I try to use the push and pop functions from the Stack.as file.  The error is this:
Error #1009: Cannot access a property or method of a null object reference.
I am not sure if I am calling the functions incorrectly in the code or if the Stack.as code I borrowed from the link above is incorrect. What I have is two buttons, "1" and "undo".  If the "1" is pressed the total value gets subtracted by 1 and number 1 gets pushed into the stack.  If "undo" is pressed then the 1 gets popped from the stack and added to the total.  Here is an implementation of my code trying to use the push and pop functions:
<fx:Script>
        <![CDATA[
            import dataStore.Node;
            import dataStore.Stack;
            public var storage:Stack;
            protected function one_clickHandler(event:MouseEvent):void
                var tot:Number =int(total.text);
                var amount:Number=int(1);
                tot=tot-1;
                total.text = String(tot);
                storage.push(amount);
            protected function undo_clickHandler(event:MouseEvent):void
                var num:Number =int(storage.pop());
                var tot:Number =int(total.text);
                tot=tot+(num);
                total.text = String(tot);
        ]]>
    </fx:Script>
I receive this error everytime I press the "1" button or the "undo" button when I am running the application.  Any info would be greatly appreciated.