Lambdas and Algorithms

<algorithm> provides ready-made operations like std::sort that work on any container's begin()/end() iterator pair, rather than you writing a sorting loop by hand.

main.cpp

Try it yourself →

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

int main() {
    vector<int> numbers = {5, 2, 8, 1, 9};
    sort(numbers.begin(), numbers.end());

    for (int n : numbers) {
        cout << n << " ";
    }
    cout << endl;
    return 0;
}

Output

1 2 5 8 9

Lambda expressions

A lambda, written [capture](params) { body }, is an anonymous inline function — the [capture] list says which surrounding variables it can see. Combined with an algorithm like std::find_if, a lambda lets you express a custom condition without writing a separate named function just for that one use.

main.cpp

Try it yourself →

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

int main() {
    vector<int> numbers = {1, 2, 3, 4, 5};
    int threshold = 3;

    auto it = find_if(numbers.begin(), numbers.end(), [threshold](int n) {
        return n > threshold;
    });

    if (it != numbers.end()) {
        cout << "First number greater than " << threshold << " is " << *it << endl;
    }
    return 0;
}

Output

First number greater than 3 is 4

Next: smart pointers — the modern, RAII-based alternative to manual new and delete.

Practice exercise

Given vector<int> numbers = {1, 2, 3, 4}, build a new vector containing each number squared, then print all of them separated by spaces.

← STL Containers and Iterators Smart Pointers →