STL

STL stands for the Standard Template Library
The STL is a library in C++ that provides a collection of generic algorithms and data structures.
It is part of the C++ standard library and consists of various template classes and functions.
The STL promotes code reuse, flexibilty, and efficiency by providing ready-to-use algorithms and data structures.
Key components of the STL include containers, algorithms, and iterators.

Containers

Containers are data structures provided by the STL to store and organize data efficiently.
The STL provides various container types, each with its own characteristics and use cases.
Commonly used containers include 'vector', 'list', 'map', 'set', 'queue', 'stack', and more.
Containers provide different interfaces and operations to manipulate and access their elements.
Containers can be categorized as sequence containers, associative containers, and container adaptors.

Vectors

'vector' is a dynamic array that grows or shrinks automatically as elements are added or removed.
It provides efficient random access to elements using indices.
Insertion and deletion at the end of a 'vector' are fast, but insertion/deletion in the middle is slower.
It provides a 'size()' function to get the number of elements and supports resizing, sorting and other operations.

Simple program ↓

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

int main()
{
    vector<int> vec = {10, 20, 30};
    vec.push_back(40);
    vec.push_back(50);
    // vec.pop_back(); // remove the last element

    // Access elements using indexing
    cout << "Element at index 1: " << vec[1] << endl;

    // Iterate over the vector using a for loop
    cout << "Elements: ";
    for (int i = 0; i < vec.size(); ++i)
    {
        cout << vec[i] << " ";
    }
    cout << endl;

    // Get the size of the vector
    cout << "Size: " << vec.size() << endl;

    // Clear the vector
    vec.clear();
    cout << "Size after clearing: " << vec.size() << endl;

    return 0;
}

List

'list' is a doubly-linked list where each element points to its previous and next elements.
It supports efficient insertion and deletion at any position, including the beginning and end.
Random access is not available in 'list', so indexing and direct element access is not possible.
'list' provides constant-time insertion and deletion operations, but traversal is slower compared to 'vector'.

Simple program ↓

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

int main()
{
    list<int> myList = {5, 10, 20};

    // Access elements
    cout << "First element: " << myList.front() << endl;
    cout << "Last element: " << myList.back() << endl;

    // Iterate over the list using a for loop
    cout << "Elements: ";
    for (const auto element : myList)
    {
        cout << element << " ";
    }
    cout << endl;

    // Insert an element at a specific position
    auto it = next(myList.begin()); // Get iterator to the second element
    myList.insert(it, 15);

    // Remove an element from the list
    myList.pop_front();

    // Check if the list is empty
    if (myList.empty())
    {
        cout << "List is empty" << endl;
    }
    else
    {
        cout << "List is not empty" << endl;
    }

    return 0;
}

Map

'map' is an associative container that stores key-value pairs, where each key is unique.
It provides efficient lookup, insertion, and deletion based on the key.
Elements in 'map' are automatically sorted by the key in ascending order.
'mapl provides a convenient way to store and retrieve data based on a unique indentifier (key).

Simple program ↓

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

int main()
{
    map<string, int> myMap = {{"John", 25}, {"Alice", 30}, {"Bob", 40}};

    // Access values using keys
    cout << "Age of Alice: " << myMap["Alice"] << endl;

    // Iterate over the map using a for loop
    cout << "Name - Age pairs: ";
    for (const auto &pair : myMap)
    {
        cout << pair.first << ":" << pair.second << " ";
    }
    cout << endl;

    // Check if a key exists in the map
    string name = "John";
    if (myMap.count(name) > 0)
    {
        cout << name << " exists in the map" << endl;
    }
    else
    {
        cout << name << " does not exist in the map" << endl;
    }

    // Erase an element from the map
    myMap.erase("Bob");

    return 0;
}