
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


NewList MyStack()
 
Procedure Push(n)
  Shared MyStack()
  LastElement(MyStack())
  AddElement(MyStack())
  MyStack()=n
EndProcedure
 
Procedure Pop()
  Shared MyStack()
  Protected n
  If FirstElement(MyStack())  ; e.g. Stack not empty
    n=MyStack()
    DeleteElement(MyStack(),1)
  Else
    Debug "Pop(), out of range. Error at line "+str(#PB_Compiler_Line)
  EndIf
  ProcedureReturn n
EndProcedure
 
Procedure Empty()
  Shared MyStack()
  If  ListSize(MyStack())=0
    ProcedureReturn #True
  EndIf
  ProcedureReturn #False
EndProcedure
 
;----   Example of implementation ----
Push(3)
Push(1)
Push(4)
While Not Empty()
  Debug Pop()
Wend
;----   Now an extra Pop(), e.g. one to many ----
Debug Pop()