# What Is the Data Structure of Stack?

//

Larry Thompson

When it comes to data structures, one of the most fundamental concepts is the stack. A stack is a linear data structure that follows a specific order in which operations are performed. It operates on the principle of Last-In-First-Out (LIFO), meaning that the last element added to the stack is the first one to be removed.

## The Basics

The stack consists of two primary operations: push and pop. The push operation adds an element to the top of the stack, while the pop operation removes the topmost element from the stack.

A visual representation of a stack can be imagined as a vertical structure with elements stacked on top of each other. The topmost element can be accessed and manipulated, while all other elements below it remain hidden until they are removed from the stack.

## Stack Implementation

In programming, stacks can be implemented using various data structures such as arrays or linked lists. However, for simplicity, we’ll focus on the array-based implementation in this article.

The array-based implementation:

To implement a stack using an array, we need to define an array and keep track of its topmost element using a variable called top. Initially, when the stack is empty, the value of top is set to -1.

``````
int MAX_SIZE = 100; // maximum size of stack
int[] stack = new int[MAX_SIZE]; // initialize an empty array
int top = -1; // initialize top as -1
```
```

The push operation:

To add an element to the stack, we increment top, then assign the new element to the array at the index top.

``````
void push(int element) {
if (top == MAX_SIZE - 1) {
// handle stack overflow
return;
}

stack[++top] = element;
}
```
```

The pop operation:

To remove an element from the stack, we retrieve the topmost element from the array at index top, then decrement top.

``````
int pop() {
if (top == -1) {
// handle stack underflow
return -1;
}

return stack[top--];
}
```
```

## Common Applications of Stacks

Stacks find applications in various domains of computer science. Some common use cases include:

• Evaluation of expressions: Stacks are used to evaluate arithmetic expressions involving parentheses, operators, and operands.
• Function call and recursion: Stacks are used to store function calls during recursive function execution.
• Backtracking algorithms: Stacks are utilized in backtracking algorithms to store potential solutions and track previous states.
• Undo/Redo functionality: Stacks can be employed to implement undo and redo operations in applications.

## In Conclusion

A stack is a crucial data structure that plays a significant role in many algorithms and applications. Understanding its underlying principles and implementation is essential for any programmer or computer scientist.

We’ve explored the basics of stacks, including their data structure, implementation using arrays, and common applications. Now, armed with this knowledge, you can confidently utilize stacks in your own projects and algorithms.