🔴 Advanced · Lesson 60

Lambda Expressions

What is Lambda Expressions?

Lambda Expressions
A lambda expression is an unnamed function written directly where it is needed. It is commonly used with STL algorithms.

Level
🔴 STL, Modern C++ and Projects

Example File
lambda.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
lambda	Lambda Expressions programming में Lambda use होता है।
capture	Lambda Expressions programming में Capture use होता है।
anonymous function	Lambda Expressions programming में Anonymous function use होता है।
predicate	Lambda Expressions programming में Predicate use होता है।

Syntax / Pattern

C++

[capture](parameters){ body }

Example Program

main.cpp

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
    vector<int> v = {1,2,3,4};
    int even = count_if(v.begin(), v.end(), [](int x){ return x%2==0; });
    cout << even;
}

Expected Output

Program Explanation

Lambda checks whether a number is even.
count_if counts elements satisfying the condition.

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?

custom sorting
filtering
callbacks

Common Mistakes

Writing unreadable long lambdas.
Forgetting capture when using outside variables.

Practice Tasks

Use lambda to count marks above 80.
Sort strings by length.

Summary

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