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FIFO (First-In-First-Out) approach in Programming
  • Difficulty Level : Basic
  • Last Updated : 16 Apr, 2019

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:

  1. Data Structures

    Certain data structures like Queue and other variants of Queue uses FIFO approach for processing data.

  2. 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.

  3. 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++

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// 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

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Java

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// 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);
    }
}

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C#

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// 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

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Output:

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

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