🔴 Advanced · Lesson 55

list and deque in STL

What is list and deque in STL?

list and deque in STL
list is a doubly linked list and deque is a double-ended queue. They are useful when frequent insertion/deletion is required.

Level
🔴 STL, Modern C++ and Projects

Example File
list-deque.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
list	List used in list and deque in STL programming.
deque	Deque used in list and deque in STL programming.
push_front	Push_front used in list and deque in STL programming.
push_back	Push_back used in list and deque in STL programming.
iterator	Iterator used in list and deque in STL programming.

Syntax / Pattern

list<int> l; deque<int> d;

Example Program

#include <iostream>
#include <deque>
using namespace std;
int main(){
    deque<int> d;
    d.push_front(10);
    d.push_back(20);
    cout << d.front() << " " << d.back();
}

Expected Output

10 20

Program Explanation

deque allows insertion at both front and back.
front() and back() read end elements.

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?

queue systems
browser history
sliding window

Common Mistakes

Using list when indexing is needed often.
Assuming list has fast random access.

Practice Tasks

Compare vector and list.
Use deque for ticket queue.

Summary

list and deque in STL 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.