Lambdas

Overview

Lambdas (C++11) are anonymous, inline functions. They are heavily used with STL algorithms (like `sort` or `count_if`) to provide custom logic on the fly without writing a whole new function.

Syntax

cpp

// Syntax: [captures] (parameters) -> return_type { body }

auto add = [](int a, int b) { 
    return a + b; 
};

cout << add(5, 3); // 8

// Captures allow access to variables outside the lambda
int multiplier = 10;
auto scale = [multiplier](int val) {
    return val * multiplier; 
};

Common Pitfalls

Capturing a local variable by reference `[&]` in a lambda, and then returning that lambda from a function. The local variable dies, leaving the lambda with a dangling reference.

Interview Tips

Understand the Capture Clause: `[=]` captures everything by value (read-only copy). `[&]` captures everything by reference (can modify original variables).

Real-World Example

Sorting a vector of objects using a lambda.

example

cpp

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

struct Player { string name; int score; };

int main() {
    vector<Player> players = {{"Alice", 50}, {"Bob", 90}, {"Charlie", 70}};
    
    // Sort by score descending using a lambda
    sort(players.begin(), players.end(), [](const Player& a, const Player& b) {
        return a.score > b.score;
    });
    
    for (const auto& p : players) {
        cout << p.name << ": " << p.score << endl;
    }
    return 0;
}

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