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++ 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 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);
    }
}

# 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# 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

<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>

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)