🔴 Advanced · Lesson 56

Stack, Queue and Priority Queue

What is Stack, Queue and Priority Queue?

Stack, Queue and Priority Queue
Stack follows LIFO, queue follows FIFO and priority queue removes elements by priority. These are important data structures in STL.

Level
🔴 STL, Modern C++ and Projects

Example File
stack-queue.cpp

Main Focus
Concept + syntax + practical C++ program

Why should you learn this?

It helps you write correct and readable C++ programs.
It is used repeatedly in school practicals, projects and competitive programming.
It builds the base for advanced topics such as OOP, STL and data structures.

Important Terms

Term	Meaning / Use
stack	Stack used in Stack, Queue and Priority Queue programming.
queue	Queue used in Stack, Queue and Priority Queue programming.
priority_queue	Priority_queue used in Stack, Queue and Priority Queue programming.
LIFO	Lifo used in Stack, Queue and Priority Queue programming.
FIFO	Fifo used in Stack, Queue and Priority Queue programming.

Syntax / Pattern

stack<int> s; queue<int> q; priority_queue<int> pq;

Example Program

#include <iostream>
#include <stack>
using namespace std;
int main(){
    stack<int> s;
    s.push(10); s.push(20);
    cout << s.top();
}

Expected Output

Program Explanation

Last inserted element 20 is on top.
Stack follows Last In First Out.

Exam Tip: In C++ practical answers, write the logic first, then the program, then expected output. For theory, always include one suitable example.

Where will you use it?

undo feature
printing queue
ranking systems

Common Mistakes

Calling top() on empty stack.
Confusing stack with queue.

Practice Tasks

Reverse numbers using stack.
Simulate student queue.

Summary

Stack, Queue and Priority Queue is an important C++ topic. Learn the definition, understand the syntax, run the example program and then solve the practice tasks to make the concept strong.