Basic Operations in Stack Data Structure with Implementations

In order to make manipulations in a stack, there are certain operations provided to us for Stack, which include:

• push() to insert an element into the stack
• pop() to remove an element from the stack
• top() Returns the top element of the stack.
• isEmpty() returns true if the stack is empty else false.
• size() returns the size of the stack.

In this post, we will see how to perform these operations on Stack.

Push Operation in Stack:

Push operation adds an item to the stack.

If the stack is full, then it is said to be an Overflow condition.

Below is a sample program to show Push operation in Stack.

C++

#include <bits/stdc++.h> 
using namespace std; 

int main() 
{ 

    stack<int> s; // creating a stack of integers 

    s.push(1); // This pushes 1 to the stack top 

    s.push(2); // This pushes 2 to the stack top 

    s.push(3); // This pushes 3 to the stack top 

    s.push(4); // This pushes 4 to the stack top 

    s.push(5); // This pushes 5 to the stack top 

    // printing the stack 

    while (!s.empty()) { 
        cout << s.top() << " "; 
        s.pop(); 
    } 

    // The above loop prints "5 4 3 2 1" 
}

Java

import java.util.Stack;

public class StackExample {
    public static void main(String[] args) {
        Stack<Integer> s = new Stack<>(); // Creating a stack of integers

        s.push(1); // This pushes 1 to the stack top
        s.push(2); // This pushes 2 to the stack top
        s.push(3); // This pushes 3 to the stack top
        s.push(4); // This pushes 4 to the stack top
        s.push(5); // This pushes 5 to the stack top

        // Printing the stack in reverse order
        while (!s.isEmpty()) {
            System.out.print(s.pop() + " ");
        }

        // The above loop prints "5 4 3 2 1"
    }
}

Python3

# Python Code:
stack = []

stack.append(1) # This pushes 1 to the stack top

stack.append(2) # This pushes 2 to the stack top

stack.append(3) # This pushes 3 to the stack top

stack.append(4) # This pushes 4 to the stack top

stack.append(5) # This pushes 5 to the stack top

# printing the stack

while stack:
    print(stack[-1], end=" ")
    stack.pop()

# The above loop prints "5 4 3 2 1"

# This code is contributed by Sakshi

C#

using System;
using System.Collections.Generic;

class Program {
    static void Main()
    {
        Stack<int> s = new Stack<int>(); // Creating a stack
                                         // of integers

        s.Push(1); // Pushing 1 to the stack top
        s.Push(2); // Pushing 2 to the stack top
        s.Push(3); // Pushing 3 to the stack top
        s.Push(4); // Pushing 4 to the stack top
        s.Push(5); // Pushing 5 to the stack top

        // Printing the stack
        while (s.Count > 0) {
            Console.Write(
                s.Peek()
                + " "); // Peek() gets the top element
                        // without removing it
            s.Pop(); // Pop() removes the top element
        }

        // The above loop prints "5 4 3 2 1"
    }
}

Javascript

class Stack {
    constructor() {
        this.stack = [];
    }

    push(value) {
        this.stack.push(value); // Pushes the value to the stack top
    }

    top() {
        return this.stack[this.stack.length - 1]; // Returns the element at the top of the stack
    }

    pop() {
        return this.stack.pop(); // Removes and returns the top element of the stack
    }

    isEmpty() {
        return this.stack.length === 0; // Checks if the stack is empty
    }
}

function main() {
    const s = new Stack(); // Creating a stack

    s.push(1); // Pushing 1 to the stack top
    s.push(2); // Pushing 2 to the stack top
    s.push(3); // Pushing 3 to the stack top
    s.push(4); // Pushing 4 to the stack top
    s.push(5); // Pushing 5 to the stack top

    // Printing the stack
    while (!s.isEmpty()) {
        console.log(s.top() + " "); // Outputting the top element
        s.pop(); // Removing the top element
    }
    // The above loop prints "5 4 3 2 1"
}

main(); // Calling the main function

Output

5 4 3 2 1 

Pop Operation in Stack:

Pop operation is used to remove an item from the stack.

The items are popped in the reversed order in which they are pushed. If the stack is empty, then it is said to be an Underflow condition.

Below is a sample program to show Pop operation in Stack.

C++

#include <bits/stdc++.h>
using namespace std;

int main()
{
    stack<int> s; // creating a stack of integers

    s.push(1); // This pushes 1 to the stack top
    s.push(2); // This pushes 2 to the stack top
    s.push(3); // This pushes 3 to the stack top
    s.push(4); // This pushes 4 to the stack top
    s.push(5); // This pushes 5 to the stack top

    // Now, let us remove elements from the stack using pop function
    while (!s.empty()) {
        cout << s.top() << " ";
        s.pop(); // removes the top element from the stack
    }
}

Java

import java.util.Stack;

public class Main {
    public static void main(String[] args)
    {
        Stack<Integer> s = new Stack<>(); // Creating a stack of integers

        s.push(1); // Pushing 1 to the stack top
        s.push(2); // Pushing 2 to the stack top
        s.push(3); // Pushing 3 to the stack top
        s.push(4); // Pushing 4 to the stack top
        s.push(5); // Pushing 5 to the stack top

        // Removing elements from the stack using the pop function
        while (!s.empty()) {
            System.out.print(s.peek() + " "); // Displaying the top element without removing it
            s.pop(); // Removes the top element from the stack
        }
    }
}

Python3

stack = []

stack.append(1) # This pushes 1 to the stack top
stack.append(2) # This pushes 2 to the stack top
stack.append(3) # This pushes 3 to the stack top
stack.append(4) # This pushes 4 to the stack top
stack.append(5) # This pushes 5 to the stack top

# Now, let us remove elements from the stack using pop function
while stack:
    print(stack[-1], end=" ")
    stack.pop() # removes the top element from the stack

C#

using System;
using System.Collections.Generic;

class Program {
    static void Main()
    {
        // Creating a stack of integers
        Stack<int> s = new Stack<int>();

        // Pushing elements onto the stack
        s.Push(1); // This pushes 1 to the stack top
        s.Push(2); // This pushes 2 to the stack top
        s.Push(3); // This pushes 3 to the stack top
        s.Push(4); // This pushes 4 to the stack top
        s.Push(5); // This pushes 5 to the stack top

        // Removing elements from the stack using Pop function
        while (s.Count > 0) {
            Console.Write(s.Peek() + " "); // Displaying the top element without removing it
            s.Pop(); // Removes the top element from the stack
        }
    }
}

Javascript

// Creating a stack
let stack = [];

// Pushing elements to the stack
stack.push(1); // This pushes 1 to the stack top
stack.push(2); // This pushes 2 to the stack top
stack.push(3); // This pushes 3 to the stack top
stack.push(4); // This pushes 4 to the stack top
stack.push(5); // This pushes 5 to the stack top

// Removing elements from the stack using pop function
while (stack.length > 0) {
    console.log(stack[stack.length - 1]); // Print the top element
    stack.pop(); // Removes the top element from the stack
}

Output

5 4 3 2 1 

Top Operation in Stack:

Top operation is used to return the top element of the stack.

Below is a sample program to show Pop operation in Stack.

C++

#include <bits/stdc++.h> 
using namespace std; 

int topElement(stack<int>& s) { return s.top(); } 

int main() 
{ 

    stack<int> s; // creating a stack of integers 

    s.push(1); // This pushes 1 to the stack top 
    cout << topElement(s) 
        << endl; // Prints 1 since 1 is present at the 
                // stack top 

    s.push(2); // This pushes 2 to the stack top 
    cout << topElement(s) 
        << endl; // Prints 2 since 2 is present at the 
                // stack top 

    s.push(3); // This pushes 3 to the stack top 
    cout << topElement(s) 
        << endl; // Prints 3 since 3 is present at the 
                // stack top 
}

Java

import java.util.Stack;

public class StackExample {

    public static int topElement(Stack<Integer> s) {
        return s.peek();
    }

    public static void main(String[] args) {
        Stack<Integer> s = new Stack<>();

        // Pushing 1 to the stack top
        s.push(1);
        System.out.println(topElement(s)); // Prints 1

        // Pushing 2 to the stack top
        s.push(2);
        System.out.println(topElement(s)); // Prints 2

        // Pushing 3 to the stack top
        s.push(3);
        System.out.println(topElement(s)); // Prints 3
    }
}

Python3

# Python code:

def topElement(s):
    return s[-1]

s = [] # creating a stack of integers

s.append(1) # This pushes 1 to the stack top
print(topElement(s)) # Prints 1 since 1 is present at the stack top

s.append(2) # This pushes 2 to the stack top
print(topElement(s)) # Prints 2 since 2 is present at the stack top

s.append(3) # This pushes 3 to the stack top
print(topElement(s)) # Prints 3 since 3 is present at the stack top

# This code is contributed by Sakshi

C#

using System;
using System.Collections.Generic;

class Program
{
    static int TopElement(Stack<int> s)
    {
        return s.Peek();
    }

    static void Main()
    {
        Stack<int> s = new Stack<int>(); // creating a stack of integers

        s.Push(1); // This pushes 1 to the stack top
        Console.WriteLine(TopElement(s)); // Prints 1 since 1 is present at the stack top

        s.Push(2); // This pushes 2 to the stack top
        Console.WriteLine(TopElement(s)); // Prints 2 since 2 is present at the stack top

        s.Push(3); // This pushes 3 to the stack top
        Console.WriteLine(TopElement(s)); // Prints 3 since 3 is present at the stack top
    }
}

Javascript

function topElement(s) {
    return s[s.length - 1];
}

// Main function
function main() {
    let s = []; // Creating an array to act as a stack

    s.push(1); // Pushing 1 to the stack
    console.log(topElement(s)); // Prints 1 since 1 is at the top of the stack

    s.push(2); // Pushing 2 to the stack
    console.log(topElement(s)); // Prints 2 since 2 is at the top of the stack

    s.push(3); // Pushing 3 to the stack
    console.log(topElement(s)); // Prints 3 since 3 is at the top of the stack
}

// Calling the main function
main();
//THis code is contributed by Utkarsh

Output

1
2
3

isEmpty Operation in Stack:

isEmpty operation is a boolean operation that is used to determine if the stack is empty or not.

This operation will return true if the stack is empty, else false.

Below is a sample program to show Pop operation in Stack.

C++

#include <bits/stdc++.h> 
using namespace std; 

bool isEmpty(stack<int>& s) 
{ 

    bool isStackEmpty 
        = s.empty(); // checking whether stack is empty or 
                    // not and storing it into isStackEmpty 
                    // variable 

    return isStackEmpty; // returning bool value stored in 
                        // isStackEmpty 
} 

int main() 
{ 

    stack<int> s; 

    // The if - else conditional statements below prints 
    // "Stack is empty." 
    if (isEmpty(s)) { 
        cout << "Stack is empty." << endl; 
    } 
    else { 
        cout << "Stack is not empty." << endl; 
    } 

    s.push(1); // Inserting value 1 to the stack top 

    // The if - else conditional statements below prints 
    // "Stack is not empty." 
    if (isEmpty(s)) { 
        cout << "Stack is empty." << endl; 
    } 
    else { 
        cout << "Stack is not empty." << endl; 
    } 
}

Java

import java.util.Stack;

public class Main {
    public static boolean isEmpty(Stack<Integer> s) {
        return s.empty();
    }

    public static void main(String[] args) {
        Stack<Integer> s = new Stack<>();

        if (isEmpty(s)) {
            System.out.println("Stack is empty.");
        } else {
            System.out.println("Stack is not empty.");
        }

        s.push(1);

        if (isEmpty(s)) {
            System.out.println("Stack is empty.");
        } else {
            System.out.println("Stack is not empty.");
        }
    }
}

Python3

# Python Code:
def isEmpty(s):
    isStackEmpty = len(s) == 0 # checking whether stack is empty or 
                               # not and storing it into isStackEmpty variable
    return isStackEmpty # returning bool value stored in isStackEmpty

s = []

# The if - else conditional statements below prints "Stack is empty."
if isEmpty(s):
    print("Stack is empty.")
else:
    print("Stack is not empty.")

s.append(1) # Inserting value 1 to the stack top

# The if - else conditional statements below prints "Stack is not empty."
if isEmpty(s):
    print("Stack is empty.")
else:
    print("Stack is not empty.")
    
# This code is contributed by Sakshi

C#

using System;
using System.Collections.Generic;

class Program
{
    // Function to check if a stack is empty
    static bool IsEmpty(Stack<int> s)
    {
        return s.Count == 0;
    }

    static void Main()
    {
        Stack<int> s = new Stack<int>();

        // Check if the stack is empty
        if (IsEmpty(s))
        {
            Console.WriteLine("Stack is empty.");
        }
        else
        {
            Console.WriteLine("Stack is not empty.");
        }

        // Push a value (1) onto the stack
        s.Push(1);

        // Check if the stack is empty after pushing a value
        if (IsEmpty(s))
        {
            Console.WriteLine("Stack is empty.");
        }
        else
        {
            Console.WriteLine("Stack is not empty.");
        }
    }
}

Javascript

function isEmpty(stack) {
    // checking whether stack is empty or not
    return stack.length === 0;
}

function main() {
    const s = [];

    // The if - else conditional statements below prints "Stack is empty."
    if (isEmpty(s)) {
        console.log("Stack is empty.");
    } else {
        console.log("Stack is not empty.");
    }

    s.push(1); // Inserting value 1 to the stack top

    // The if - else conditional statements below prints "Stack is not empty."
    if (isEmpty(s)) {
        console.log("Stack is empty.");
    } else {
        console.log("Stack is not empty.");
    }
}

// Run the main function
main();
//This code is contributed by Monu.

Output

Stack is empty.
Stack is not empty.

size() Operation in Stack:

Size operation in Stack is used to return the count of elements that are present inside the stack. 

Below is a sample program to show Pop operation in Stack.

C++

#include <bits/stdc++.h> 
using namespace std; 

int main() 
{ 

    stack<int> s; // creating a stack of integers 

    cout << s.size() 
        << endl; // Prints 0 since the stack is empty 

    s.push(1); // This pushes 1 to the stack top 
    s.push(2); // This pushes 2 to the stack top 
    cout << s.size() << endl; // Prints 2 since the stack 
                            // contains two elements 

    s.push(3); // This pushes 3 to the stack top 
    cout << s.size() << endl; // Prints 3 since the stack 
                            // contains three elements 
}

Java

import java.util.Stack;

public class Main {
    public static void main(String[] args) {
        Stack<Integer> s = new Stack<>(); // creating a stack of integers

        System.out.println(s.size()); // Prints 0 since the stack is empty

        s.push(1); // This pushes 1 to the stack top
        s.push(2); // This pushes 2 to the stack top
        System.out.println(s.size()); // Prints 2 since the stack contains two elements

        s.push(3); // This pushes 3 to the stack top
        System.out.println(s.size()); // Prints 3 since the stack contains three elements
    }
}

Python3

# PYthon Code:
stack = [] # creating an empty list as a stack

print(len(stack)) # Prints 0 since the stack is empty

stack.append(1) # This appends 1 to the stack
stack.append(2) # This appends 2 to the stack
print(len(stack)) # Prints 2 since the stack contains two elements

stack.append(3) # This appends 3 to the stack
print(len(stack)) # Prints 3 since the stack contains three element

# This code is contributed by Sakshi

C#

using System;
using System.Collections.Generic;

public class Program
{
    public static void Main(string[] args)
    {
        Stack<int> s = new Stack<int>(); // creating a stack of integers 

        Console.WriteLine(s.Count); // Prints 0 since the stack is empty 

        s.Push(1); // This pushes 1 to the stack top 
        s.Push(2); // This pushes 2 to the stack top 
        Console.WriteLine(s.Count); // Prints 2 since the stack contains two elements 

        s.Push(3); // This pushes 3 to the stack top 
        Console.WriteLine(s.Count); // Prints 3 since the stack contains three elements 
    }
}
//This code is contribiuted by Kishan.

Javascript

let stack = []; // Creating an array to simulate a stack

console.log(stack.length); // Prints 0 since the stack is empty

stack.push(1); // This pushes 1 to the stack top
stack.push(2); // This pushes 2 to the stack top
console.log(stack.length); // Prints 2 since the stack contains two elements

stack.push(3); // This pushes 3 to the stack top
console.log(stack.length); // Prints 3 since the stack contains three elements
//This code is contributed by Aman.

Output

0
2
3