In this article, we will explore the concept of Abstract Data Types (ADTs) and discuss one of the most commonly used ADTs in computer science – the stack data structure. A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle, meaning that the last element added to the stack will be the first one to be removed.

## Abstract Data Types (ADTs)

**Abstract Data Type** refers to a high-level description of a data type from a user’s perspective. It defines the behavior and properties of a data type without specifying its implementation details. ADTs allow us to focus on how data should be used rather than how it is implemented.

ADTs can be implemented using different data structures, such as arrays, linked lists, or trees. The choice of implementation depends on the specific requirements and constraints of an application.

## The Stack Data Structure

**A stack** is a fundamental data structure that follows a __Last-In-First-Out (LIFO)__ approach. It can be visualized as a stack of books where you can only add or remove books from the top.

The two main operations performed on a stack are:

**Push:**Adds an element to the top of the stack.**Pop:**Removes and returns the topmost element from the stack.

Apart from these core operations, stacks also support other operations:

**Peek/Top:**Returns the value of the topmost element without removing it.**isEmpty:**Checks if the stack is empty or not.**Size:**Returns the number of elements present in the stack.

### Implementation of Stack

A stack can be implemented using an array or a linked list. Here, we will discuss the array-based implementation.

To implement a stack using an array, we need to keep track of the top element and the size of the stack. The top element represents the index of the last element pushed onto the stack.

**Operations on Stack:**

__Push Operation:__

The push operation adds an element to the top of the stack. In an array-based implementation, we increment the top index and insert the new element at that position.

```
function push(element) {
if (top == MAX_SIZE - 1) {
// Overflow condition
console.log("Stack Overflow");
return;
}
top++;
stack[top] = element;
}
```

__Pop Operation:__

The pop operation removes and returns the topmost element from the stack. In an array-based implementation, we return the element at the current top index and decrement the top index by one.

```
function pop() {
if (top == -1) {
// Underflow condition
console.log("Stack Underflow");
return null;
}
var poppedElement = stack[top];
top--;
return poppedElement;
}
```

### Conclusion

The stack data structure is widely used in various algorithms and applications. Its simplicity and efficiency make it a popular choice for solving different problems. Understanding ADTs like stacks is crucial for developing efficient and optimized software solutions.

Now that you have a good understanding of what ADTs are and the operations of the stack data structure, you can start exploring its applications in different programming scenarios.