What Is Stack in Data Structure Notes?

A **stack** is a linear data structure that follows the Last-In-First-Out (LIFO) principle. It is an abstract data type and is commonly used in programming and computer science. In a stack, elements are added to and removed from the top of the stack.

## Stack Operations

A stack supports two main operations:

**Push:**This operation adds an element to the top of the stack.**Pop:**This operation removes the topmost element from the stack.

You can visualize a stack as a vertical structure where elements are stacked one on top of another. The element at the bottom is called the base, while the element at the top is called the top or head of the stack.

### Stack Implementation

A stack can be implemented using various data structures such as arrays and linked lists. Let’s take a look at how we can implement a stack using an array.

```
// Stack implementation using an array
class Stack {
constructor() {
this.items = [];
}
push(element) {
this.items.push(element);
}
pop() {
if (this.isEmpty()) {
return "Underflow";
}
return this.pop();
}
isEmpty() {
return this.length === 0;
}
// Other utility methods like peek, size, etc.
}
```

The above code snippet shows a basic implementation of a stack using an array in JavaScript. The `push()`

method is used to add elements to the top of the stack, while `pop()`

is used to remove the topmost element. The `isEmpty()`

method checks if the stack is empty or not.

### Stack Applications

Stacks have various applications in computer science and programming. Some common areas where stacks are used include:

**Expression evaluation:**Stacks are used to evaluate arithmetic expressions, infix to postfix conversion, and more.**Function call stack:**Stacks are used to store information about function calls and their parameters.**Undo/Redo functionality:**Stacks can be used to implement undo/redo operations in applications.**Browsing history:**Web browsers use stacks to keep track of visited web pages.

These are just a few examples of how stacks can be utilized. Understanding the stack data structure is essential for building efficient algorithms and solving programming problems.

## In Conclusion

A stack is a fundamental data structure that follows the Last-In-First-Out principle. It supports two main operations: push and pop. Stacks can be implemented using arrays or linked lists, and they have various applications in computer science and programming domains.

If you want to dive deeper into data structures, make sure to explore other important concepts such as queues, linked lists, trees, and graphs. These topics will help you develop a strong foundation in computer science and problem-solving skills.