 
      
      stackProvides Stack data type
class stackThis class does not inherit to any class.
construct() — The constructor. Create an instance of class stack        getsize() — Get the size of the Stack        isempty() — Check whether the size of the Stack is empty or not        makeempty() — Make the Stack empty        pop() — Retrieve and remove the top of the Stack, or return nothing if the Stack is empty        push() — Push a new element into the top of the Stack        toarray() — Create an array containing all of the elements in the Stack        top() — Retrieve but not remove the top of the Stack, or return nothing if the Stack is empty