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

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); 
    } 
} 

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("
removed element-" + removedele + "
");  
        foreach(int s in q)  
                Console.Write(s + " ");  
  
        // To view the head of queue  
        int head = q.Peek();  
        Console.Write("
head 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("
Size of queue-" + size);  
    }  
}  
  
// This code has been contributed by 29AjayKumar 

Output:

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

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

C++

Java

C#

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