# What Is Stack ADT in Data Structure?

//

Larry Thompson

The Stack Abstract Data Type (ADT) is a commonly used data structure in computer science. It follows the Last-In-First-Out (LIFO) principle, where the last element inserted is the first one to be removed. In this article, we will explore what a Stack ADT is, its operations, and how it can be implemented in different programming languages.

## Operations of a Stack ADT

A Stack ADT supports various operations that allow us to interact with the data structure. Let’s take a look at some of these key operations:

• Push: This operation adds an element to the top of the stack.
• Pop: This operation removes and returns the element from the top of the stack.
• Peek (or Top): This operation returns the element at the top of the stack without removing it.
• isEmpty: This operation checks whether the stack is empty or not.

A Stack ADT can be implemented using different data structures such as arrays or linked lists. Let’s discuss two common implementations:

### Array-based Implementation:

In this implementation, we use an array to store elements of the stack. We also maintain a variable to keep track of the topmost element in the stack. Here’s an example implementation in pseudo-code:

```  ```
Data Structure:
- Array: elements
- Integer: top

Operations:
- Push(element):
- Increment top by 1
- Set elements[top] as element

- Pop():
- Return elements[top] and decrement top by 1

- Peek():
- Return elements[top]

- isEmpty():
- Return true if top equals -1, else return false
```
```

In this implementation, we use a linked list to store the elements of the stack. Each node in the linked list represents an element, and the top is represented by the head of the linked list. Here’s an example implementation in pseudo-code:

```  ```
Data Structure:

Operations:
- Push(element):
- Create a new node with the given element
- Set the new node's next pointer to head
- Set head as the new node

- Pop():
- If head is null, return null
- Store head's element in a variable
- Return the stored element

- Peek():

- isEmpty():
- Return true if head is null, else return false
```
```

Both implementations have their advantages and disadvantages. The array-based implementation provides constant-time access to elements but has a fixed size. On the other hand, the linked list-based implementation can dynamically grow or shrink but requires extra memory for storing pointers.

The Stack ADT has various applications across different domains, including:

• Expression evaluation and syntax parsing.
• Undo and redo functionalities in text editors or graphic applications.
• Implementing function calls and recursion in programming languages.
• Balancing symbols such as parentheses, brackets, and braces.

Understanding the Stack ADT is essential for any programmer or computer science enthusiast. It provides a fundamental understanding of how data can be organized and accessed efficiently. By incorporating the LIFO principle, the Stack ADT enables elegant solutions to a wide range of problems.

Now that you have a solid understanding of the Stack ADT, you can confidently apply it in your future programming endeavors!