C++ Queues

C++ Queues: First-In, First-Out (FIFO)

If a Stack is a pile of pancakes, a Queue is a line of people waiting at a movie theater.

A queue operates on the FIFO (First-In, First-Out) principle. The first person to enter the line is the first person to get their ticket and leave the line. In programming, the first item added to a queue is the first item to be processed.

1. Using Queues

To use a queue, include the <queue> header.

Key Operations:

• .push() - Adds an element to the back of the queue.
• .pop() - Removes an element from the front of the queue.
• .front() - Returns the first element (the one next to be processed).
• .back() - Returns the last element added.

#include <iostream>
#include <queue>
using namespace std;

int main() {
  queue<string> printJobs;
  // Add jobs to the queue
  printJobs.push("Document1.pdf");
  printJobs.push("Image_final.png");
  printJobs.push("Invoice.docx");
  // Display the next job in line
  cout << "Currently printing: " << printJobs.front() << "\n";
  // Finish the first job, remove it from the line
  printJobs.pop();
  cout << "Up next: " << printJobs.front() << "\n";
  return 0;
}

2. When Are Queues Used?

Queues are essential for scenarios where order of arrival matters:

• Printer Tasks: Processing print jobs in the order they were submitted.
• Customer Service Software: Managing support tickets (first ticket in gets priority).
• Task Scheduling: Your CPU uses complex queues to decide which background app gets processing time next!