
Data Structure

This illustrates a data structure, a means of storing data within a program.

You may see other such structures in the Data Structures category.
 Illustration of FIFO behavior
Task

Create a queue data structure and demonstrate its operations.

(For implementations of queues, see the FIFO task.)



Operations:

   push       (aka enqueue) - add element
   pop         (aka dequeue) - pop first element
   empty     - return truth value when empty


See also

 Array
 Associative array: Creation, Iteration
 Collections
 Compound data type
 Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
 Linked list
 Queue: Definition, Usage
 Set
 Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
 Stack


 
test: proc options (main);
 
 
   /* To implement a queue. */
   define structure
      1 node,
         2 value fixed,
         2 link handle(node);
   declare (head, tail, t) handle (node);
   declare null builtin;
   declare i fixed binary;
 
   head, tail = bind(:node, null:);
 
   do i = 1 to 10; /* Add ten items to the tail of the queue. */
      if head = bind(:node, null:) then
         do;
            head,tail = new(:node:);
            get list (head => value);
            put skip list (head => value);
            head => link = bind(:node, null:); /* A NULL link */
         end;
      else
         do;
            t = new(:node:);
            tail => link = t; /* Point the tail to the new node. */
            tail = t;
            tail => link = bind(:node, null:); /* Set the tail link to NULL */
            get list (tail => value) copy;
            put skip list (tail => value);
         end;
   end;
 
   /* Pop all the items in the queue. */
   put skip list ('The queue has:');
   do while (head ^= bind(:node, null:));
      put skip list (head => value);
      head = head => link;
   end;
end test;
 