
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

Implement a FIFO queue.

Elements are added at one side and popped from the other in the order of insertion.



Operations:

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


Errors:

   handle the error of trying to pop from an empty queue (behavior depends on the language and platform)


See

   Queue/Usage   for the built-in FIFO or queue of your language or standard library.


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


program queue;
 {$IFDEF FPC}{$MODE DELPHI}{$IFDEF WINDOWS}{$APPTYPE CONSOLE}{$ENDIF}{$ENDIF} 
 {$ASSERTIONS ON} 
uses Generics.Collections;
 
var
  lQueue: TQueue<Integer>;
begin
  lQueue := TQueue<Integer>.Create;
  try
    lQueue.EnQueue(1);
    lQueue.EnQueue(2);
    lQueue.EnQueue(3); 
    Write(lQueue.DeQueue:2);   // 1
    Write(lQueue.DeQueue:2);   // 2
    Writeln(lQueue.DeQueue:2); // 3
    Assert(lQueue.Count = 0, 'Queue is not empty'); // should be empty
  finally
    lQueue.Free;
  end;
end.