Stack STL in C++.

Stack STL is a very useful tool when we have to work with Stack data structure in real programming because then we do not have to implement the complete stack from the beginning each time we use them in our code. But before learning Stack STL in detail let's get a short idea about C++ STL.

The Standard Template Library (STL) in C++ is a powerful collection of template classes and functions that provides a rich set of algorithms, containers, and functionalities to facilitate generic programming. It is a fundamental part of the C++ programming language, aiming to simplify and enhance code reusability, maintainability, and efficiency.

What is Stack STL?

In the list of STL containers, we also have Stack STL which is a powerful tool that provides an efficient and easy-to-use implementation of the stack data structure. The std::stack class encapsulates the functionality of a stack, offering a convenient interface to manage data in a Last In, First Out (LIFO) manner.

std::stack abstracts the core stack operations (push, pop, top, isEmpty, and size) into intuitive member functions, simplifying the manipulation of elements in the stack. It is an adapter class that adapts an underlying container (like std::deque, std::vector, or std::list) to provide stack functionalities.

Functions Present in Stack STL.

The std::stack container adapter in C++ provides several functions to manipulate elements in a stack-like structure. Here are the functions available in std::stack:

stack.push(element): Adds an element to the top of the stack.

stack.pop(): Removes the top element from the stack.

stack.top(): Retrieves the top element from the stack without removing it.

stack.empty(): Checks if the stack is empty. Returns true if the stack is empty, else returns false.

stack.size(): Returns the number of elements in the stack.

Stack STL in C++ Program.

To use Stack STL in our code we first have to include <stack> header file and below is the syntax to declare a stack of specific type (e.g., integers).

Syntax: std::stack<dataType> myStack;

C++ Code:

// C++ Code Example of Stack STL
#include <iostream>
#include <stack>
using namespace std;

int main() {
    stack<int> myStack;

    // Pushing elements onto the stack
    myStack.push(10);
    myStack.push(20);
    myStack.push(30);

    // Accessing the top element
    cout << "Top element: " << myStack.top() << endl;

    // Popping the top element
    myStack.pop();

    // Checking if the stack is empty
    if (myStack.empty()) {
        cout << "Stack is empty\n";
    } else {
        cout << "Stack is not empty\n";
    }

    // Determining the size of the stack
    cout << "Size of stack: " << myStack.size() << endl;

    return 0;
}

Output:

Top element: 30
Stack is not empty
Size of stack: 2

Time and Space Complexity.

Time Complexity: push(), pop(), top(), empty(), and size() have constant time complexity O(1) regardless of the number of elements in the stack.

Space Complexity: The space complexity of std::stack mainly depends on the underlying container used. By default, it uses std::deque as its underlying container, which typically allocates memory in blocks. Therefore, the space complexity can be considered as O(n).

Mostly while problem-solving and in real-world applications we use STL of different data structures instead of building it from the beginning and we also encourage you to learn and use them in your code to make it more efficient but at the same time, you all should know the basic principle and working of stack and other data structure.