The STL: Containers and Algorithms

The Standard Template Library gives you tested containers and algorithms. Knowing it well is the difference between clever code and maintainable code.

Containers

• std::vector — ordered, fast to iterate.
• std::map — sorted key-value pairs.
• std::unordered_map — fast lookups without order.
• std::set — unique sorted values.

Algorithms

Include <algorithm> and <numeric> for sorting, searching and summing.

#include <algorithm>
#include <numeric>
#include <vector>

std::vector<int> scores = {88, 74, 91, 65};

std::sort(scores.begin(), scores.end());

int total = std::accumulate(scores.begin(), scores.end(), 0);

auto found = std::find(scores.begin(), scores.end(), 91);
if (found != scores.end()) {
    std::cout << "Found 91\n";
}

Lambdas

A lambda is an inline function. Use it with algorithms to express intent without a separate named function.

auto passing = std::count_if(scores.begin(), scores.end(),
    [](int score) { return score >= 70; });

std::cout << passing << " students passed\n";

Practice

1. Sort a vector of names alphabetically.
2. Count how many scores are below 50.
3. Use a map to count word frequencies.

Hands-on exercise

Given a vector of scores:
1. Sort it.
2. Print the highest and lowest.
3. Count how many are at least 70 using count_if and a lambda.

Recap

Choose the container that matches the access pattern, and use standard algorithms with lambdas for collection work.