In C++, the Standard Template Library (STL) provides a versatile container called std::stack for implementing a stack data structure. A stack is a Last-In-First-Out (LIFO) data structure, meaning that the element inserted last will be the first one to be removed. The std::stack container encapsulates this behavior and provides a simple interface for stack operations.

Declaration

#include <stack>

std::stack<int> myStack; // Declaring a stack of integers

Functions of Stack

1 push()

Inserts an element onto the top of the stack.

#include <iostream>
#include <stack>

int main() {
    std::stack<int> myStack;
    myStack.push(5); // Pushing element 5 onto the stack
    return 0;
}

Time Complexity: O(1)

2 pop()

Removes the top element from the stack. It does not return any thing.

#include <iostream>
#include <stack>

int main() {
    std::stack<int> myStack;
    myStack.push(5);
    myStack.pop(); // Removing the top element from the stack
    return 0;
}

Time Complexity: O(1)

3 top()

Accesses the top element of the stack without removing it.

#include <iostream>
#include <stack>

int main() {
    std::stack<int> myStack;
    myStack.push(5);
    int topElement = myStack.top(); // Accessing the top element of the stack
    std::cout << "Top element: " << topElement << std::endl;
    return 0;
}

// Output
Top element: 5

Time Complexity: O(1)

4 size()

Returns the number of elements in the stack

#include <iostream>
#include <stack>

int main() {
    std::stack<int> myStack;
    myStack.push(5);
    int stackSize = myStack.size(); // Getting the size of the stack
    std::cout << "Stack size: " << stackSize << std::endl;
    return 0;
}

// Output
Stack size: 1

Time Complexity: O(1)

5 empty()

Checks if the stack is empty

#include <iostream>
#include <stack>

int main() {
    std::stack<int> myStack;
    bool isEmpty = myStack.empty(); // Checking if the stack is empty
    if (isEmpty) {
        std::cout << "Stack is empty" << std::endl;
    }
    return 0;
}

// Output
Stack is empty

Time Complexity: O(1)