**What Is Stack in Data Structure PDF?**

A stack is a fundamental data structure in computer science that follows the Last-In-First-Out (LIFO) principle. It is commonly used to store and manage data in various applications.

Understanding the concept of a stack is crucial for any programmer or computer science enthusiast.

## Stack Basics

A stack can be visualized as a vertical structure where elements are added or removed from the top, known as the “top of the stack.” The operations performed on a stack include:

**Push:**Adding an element to the top of the stack.**Pop:**Removing the top element from the stack.**Peek (or Top):**Viewing the value of the top element without removing it.**isEmpty:**Checking if the stack is empty or not.

The LIFO principle ensures that when an element is added to a stack, it becomes the new top, and when an element is removed, it exposes the previous top.

## Applications of Stacks

Stacks find widespread use in various algorithms and applications. Here are some common scenarios where stacks prove valuable:

__Balanced Parentheses:__Stacks can be used to check whether parentheses in an expression are balanced or not. Opening parentheses are pushed onto the stack, and closing parentheses pop elements off the stack until either all parentheses match or an imbalance occurs.__Infix-to-Postfix Conversion:__Stacks are employed to convert mathematical expressions from infix notation (operators between operands) to postfix notation (operators after operands).This conversion allows for easier evaluation of the expression.

__Function Call Stack:__Stacks are used to manage function calls in programming languages. Each time a function is called, its local variables and return address are pushed onto the stack, and when the function returns, they are popped off.__Undo/Redo Functionality:__Stacks can be utilized to implement undo/redo functionality in applications like text editors or image editing software. Each operation is pushed onto a stack, allowing users to undo or redo changes by popping elements off the stack.

## Implementing a Stack

Stacks can be implemented using various data structures such as arrays and linked lists. The choice of implementation depends on factors like memory efficiency, ease of use, and desired operations’ time complexity.

Arrays offer a straightforward implementation of a stack. The top element can be stored in a variable, and push and pop operations can be performed by modifying the index of the top element.

However, this approach has limitations in terms of size flexibility.

Linked lists provide a dynamic implementation of stacks where nodes are linked together using pointers. The head node represents the top of the stack, and push and pop operations involve updating the head pointer accordingly.

### Conclusion

In conclusion, understanding stacks is essential for any programmer working with data structures or algorithms. The LIFO principle and various operations associated with stacks make them versatile tools in solving numerous programming problems.

By grasping the concept of stacks and their applications, programmers can enhance their problem-solving skills and develop efficient algorithms in various domains.