FIFO (First-In-First-Out) approach in Programming

Last Updated : 06 Dec, 2022

FIFO is an abbreviation for first in, first out. It is a method for handling data structures where the first element is processed first and the newest element is processed last.

Real-life example:

In this example, following things are to be considered:

There is a ticket counter where people come, take tickets and go.
People enter a line (queue) to get to the Ticket Counter in an organized manner.
The person to enter the queue first, will get the ticket first and leave the queue.
The person entering the queue next will get the ticket after the person in front of him
In this way, the person entering the queue last will the tickets last
Therefore, the First person to enter the queue gets the ticket first and the Last person to enter the queue gets the ticket last.

This is known as First-In-First-Out approach or FIFO.

Where is FIFO used:

Data Structures:
- Certain data structures like Queue and other variants of Queue uses FIFO approach for processing data.
Disk scheduling:
- Disk controllers can use the FIFO as a disk scheduling algorithm to determine the order in which to service disk I/O requests.
Communications and networking”
- Communication network bridges, switches and routers used in computer networks use FIFOs to hold data packets en route to their next destination.

Program Examples for FIFO

Program 1: Queue

C++

// C++ program to demonstrate 
// working of FIFO 
// using Queue interface in C++
 
#include<bits/stdc++.h>
using namespace std;
 
// print the elements of queue
void print_queue(queue<int> q)
{
    while (!q.empty())
    {
        cout << q.front() << " ";
        q.pop();
    }
    cout << endl;
}
 
// Driver code
int main() 
{ 
    queue<int> q ;
 
    // Adds elements {0, 1, 2, 3, 4} to queue 
    for (int i = 0; i < 5; i++) 
        q.push(i); 
 
    // Display contents of the queue. 
    cout << "Elements of queue-";
         
    print_queue(q);
 
    // To remove the head of queue. 
    // In this the oldest element '0' will be removed 
    int removedele = q.front();
    q.pop();
    cout << "removed element-" << removedele << endl; 
 
    print_queue(q);
 
    // To view the head of queue 
    int head = q.front(); 
    cout << "head of queue-" << head << endl; 
 
    // Rest all methods of collection interface, 
    // Like size and contains can be used with this 
    // implementation. 
    int size = q.size(); 
    cout << "Size of queue-" << size;
         
    return 0;
} 
 
// This code is contributed by Arnab Kundu

Java

// Java program to demonstrate
// working of FIFO
// using Queue interface in Java
 
import java.util.LinkedList;
import java.util.Queue;
 
public class QueueExample {
    public static void main(String[] args)
    {
        Queue<Integer> q = new LinkedList<>();
 
        // Adds elements {0, 1, 2, 3, 4} to queue
        for (int i = 0; i < 5; i++)
            q.add(i);
 
        // Display contents of the queue.
        System.out.println("Elements of queue-" + q);
 
        // To remove the head of queue.
        // In this the oldest element '0' will be removed
        int removedele = q.remove();
        System.out.println("removed element-" + removedele);
 
        System.out.println(q);
 
        // To view the head of queue
        int head = q.peek();
        System.out.println("head of queue-" + head);
 
        // Rest all methods of collection interface,
        // Like size and contains can be used with this
        // implementation.
        int size = q.size();
        System.out.println("Size of queue-" + size);
    }
}

Python3

# Python program to demonstrate
# working of FIFO
# using Queue interface in Python
 
q = []
 
# Adds elements {0, 1, 2, 3, 4} to queue
for i in range(5):
    q.append(i)
 
# Display contents of the queue.
print("Elements of queue-" , q)
 
# To remove the head of queue.
# In this the oldest element '0' will be removed
removedele = q.pop(0)
print("removed element-" , removedele)
 
print(q)
 
# To view the head of queue
head = q[0]
print("head of queue-" , head)
 
# Rest all methods of collection interface,
# Like size and contains can be used with this
# implementation.
size = len(q)
print("Size of queue-" , size)
 
# This code is contributed by patel2127.

C#

// C# program to demonstrate 
// working of FIFO 
using System;
using System.Collections.Generic;
 
public class QueueExample 
{ 
    public static void Main(String[] args) 
    { 
        Queue<int> q = new Queue<int>(); 
 
        // Adds elements {0, 1, 2, 3, 4} to queue 
        for (int i = 0; i < 5; i++) 
            q.Enqueue(i); 
 
        // Display contents of the queue. 
        Console.Write("Elements of queue-"); 
        foreach(int s in q) 
                Console.Write(s + " "); 
 
        // To remove the head of queue. 
        // In this the oldest element '0' will be removed 
        int removedele = q.Dequeue(); 
        Console.Write("\nremoved element-" + removedele + "\n"); 
        foreach(int s in q) 
                Console.Write(s + " "); 
 
        // To view the head of queue 
        int head = q.Peek(); 
        Console.Write("\nhead of queue-" + head); 
 
        // Rest all methods of collection interface, 
        // Like size and contains can be used with this 
        // implementation. 
        int size = q.Count; 
        Console.WriteLine("\nSize of queue-" + size); 
    } 
} 
 
// This code has been contributed by 29AjayKumar

Javascript

<script>
 
// JavaScript program to demonstrate
// working of FIFO
// using Queue interface in Java
 
let q = [];
// Adds elements {0, 1, 2, 3, 4} to queue
for (let i = 0; i < 5; i++)
    q.push(i);
 
// Display contents of the queue.
document.write("Elements of queue-[" + q.join(", ")+"]<br>");
 
// To remove the head of queue.
// In this the oldest element '0' will be removed
let removedele = q.shift();
document.write("removed element-" + removedele+"<br>");
 
document.write("["+q.join(", ")+"]<br>");
 
// To view the head of queue
let head = q[0];
document.write("head of queue-" + head+"<br>");
 
// Rest all methods of collection interface,
// Like size and contains can be used with this
// implementation.
let size = q.length;
document.write("Size of queue-" + size+"<br>");
 
 
// This code is contributed by avanitrachhadiya2155
 
</script>

Output

Elements of queue-0 1 2 3 4 
removed element-0
1 2 3 4 
head of queue-1
Size of queue-4

Complexities Analysis:

Time Complexity: O(N)
Space Complexity: O(N)

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LIFO (Last-In-First-Out) approach in Programming

FIFO (First-In-First-Out) approach in Programming

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