
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


#!/usr/bin/awk -f
 
BEGIN {
    delete q
    print "empty? " emptyP()
    print "push " push("a")
    print "push " push("b")
    print "empty? " emptyP()
    print "pop " pop()
    print "pop " pop()
    print "empty? " emptyP()
    print "pop " pop()
}
 
function push(n) {
    q[length(q)+1] = n
    return n
}
 
function pop() {
    if (emptyP()) {
        print "Popping from empty queue."
        exit
    }
    r = q[length(q)]
    delete q[length(q)]
    return r
}
 
function emptyP() {
    return length(q) == 0
}
 