🔴 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 and deque in STL programming में List use होता है।
deque	list and deque in STL programming में Deque use होता है।
push_front	list and deque in STL programming में Push_front use होता है।
push_back	list and deque in STL programming में Push_back use होता है।
iterator	list and deque in STL programming में Iterator use होता है।

Syntax / Pattern

C++

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

Example Program

main.cpp

#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 एक ज़रूरी C++ topic है। परिभाषा सीखें, syntax समझें, example program चलाएं और फिर practice tasks हल करके concept मज़बूत करें।