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The Standard Template Library (STL) provides ready-to-use data structures and algorithms. It is one of C++'s greatest strengths — you don't need to implement common data structures from scratch.

Why STL Matters

Battle-tested, optimized implementations
Generic programming — works with any data type
Reduces bugs by avoiding manual memory management
Standard across all C++ compilers and platforms

STL Components

Containers: store data (vector, map, set, etc.)
Algorithms: operate on containers (sort, find, etc.)
Iterators: traverse containers

Vector (Dynamic Array)

Vector is the default STL container. It is introduced in the Arrays & Strings topic; here we only note that it is a sequence container that grows dynamically and works with the algorithms below.

Algorithms

#include <algorithm>
sort(v.begin(), v.end());        // Sort ascending
sort(v.begin(), v.end(), greater<int>());  // Sort descending
reverse(v.begin(), v.end());     // Reverse
auto it = find(v.begin(), v.end(), 8);  // Find element
int count = std::count(v.begin(), v.end(), 5);  // Count

Other Containers

deque: double-ended queue
list: doubly-linked list
set: sorted unique elements
map: sorted key-value pairs
unordered_map: hash map (faster lookup)
stack: LIFO
queue: FIFO
priority_queue: priority-based queue

Common mistakes: using v[i] without bounds checking (v.at(i) checks) and modifying a vector while an iterator points into it, which invalidates that iterator.

Key takeaway: STL provides containers, algorithms, and iterators — use vector as your default container.

Try it: Create a vector<int>, sort it, print the smallest element with front(), and count how many times a chosen value appears.

#include <algorithm> sort(v.begin(), v.end()); // Sort ascending sort(v.begin(), v.end(), greater<int>()); // Sort descending reverse(v.begin(), v.end()); // Reverse auto it = find(v.begin(), v.end(), 8); // Find element int count = std::count(v.begin(), v.end(), 5); // Count

Other Containers

deque: double-ended queue

list: doubly-linked list

set: sorted unique elements

map: sorted key-value pairs

unordered_map: hash map (faster lookup)

stack: LIFO

queue: FIFO

priority_queue: priority-based queue

Common mistakes: using v[i] without bounds checking (v.at(i) checks) and modifying a vector while an iterator points into it, which invalidates that iterator.

Key takeaway: STL provides containers, algorithms, and iterators — use vector as your default container.

Try it: Create a vector<int>, sort it, print the smallest element with front(), and count how many times a chosen value appears.