STL Containers and Iterators

std::map<K, V> stores key-value pairs, keeping them sorted by key automatically. Iterating it with range-based for yields key-value pairs in that sorted order, with .first and .second giving you the key and value respectively.

#include <iostream>
#include <map>
#include <string>
using namespace std;

int main() {
    map<string, int> ages;
    ages["Alice"] = 30;
    ages["Bob"] = 25;

    for (const auto& pair : ages) {
        cout << pair.first << ": " << pair.second << endl;
    }
    return 0;
}

Alice: 30
Bob: 25

std::set

std::set stores unique values in sorted order, automatically discarding duplicates as they're inserted — the same underlying tree structure as map, just without a separate value attached to each key.

#include <iostream>
#include <set>
using namespace std;

int main() {
    set<int> numbers = {5, 3, 1, 4, 1, 5};
    for (int n : numbers) {
        cout << n << " ";
    }
    cout << endl;
    return 0;
}

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Every STL container — vector, map, set, and others — supports this same range-based for syntax, because they all expose the begin()/end() iterator pair that range-based for relies on under the hood.

Next: lambdas and algorithms — anonymous functions combined with the STL's own algorithm library.