What is a Stack and How to Implement Stack in C? | DeveloperIndian.com

Stacks are one of the fundamental data structures in computer science that every developer should understand. If you're looking for an in-depth explanation of what a stack is, along with an easy-to-follow implementation of stack in C, you're in the right place! In this article, we'll break down the concept of stacks, their primary operations, and guide you through a simple implementation in C.

What is a Stack?

A stack is a linear data structure that follows the LIFO (Last In, First Out) principle. This means that the last element added to the stack is the first one to be removed. Stacks are widely used in programming for tasks such as expression evaluation, backtracking, function call management, and more.

Key Features of a Stack

1. Top: Refers to the most recently added element in the stack.
2. Overflow: Occurs when trying to add an element to a full stack.
3. Underflow: Occurs when trying to remove an element from an empty stack.

Primary Stack Operations

1. Push: Add an element to the top of the stack.
2. Pop: Remove the element from the top of the stack.
3. Peek/Top: View the element at the top without removing it.
4. IsEmpty: Check if the stack is empty.
5. IsFull: Check if the stack is full.

Why Use a Stack?

Stacks are essential for various scenarios, including:

• Reversing strings.
• Managing browser history.
• Handling recursive function calls.
• Parsing expressions in compilers.

Implementation of Stack in C

Let’s dive into the implementation of a stack using arrays in C. This program allows you to perform basic stack operations such as push, pop, and show.

#include<stdio.h>
#define MAX 10

int stack[MAX], top = -1;

// Push Operation
void push(int val) {
    if (top == MAX - 1) {
        printf("\nOverflow: Stack is full");
        return;
    }
    stack[++top] = val;
}

// Pop Operation
int pop() {
    if (top == -1) {
        printf("\nUnderflow: Stack is empty");
        return -999;
    }
    return stack[top--];
}

// Display Stack
void show() {
    if (top == -1) {
        printf("\nStack is empty");
        return;
    }
    printf("\nStack elements are:");
    for (int i = top; i >= 0; i--) {
        printf(" %d", stack[i]);
    }
}

void main() {
    int no, ch;
    do {
        printf("\n1. Push");
        printf("\n2. Pop");
        printf("\n3. Show");
        printf("\n0. Exit");
        printf("\nEnter your choice: ");
        scanf("%d", &ch);

        switch (ch) {
            case 1:
                printf("\nEnter number to push: ");
                scanf("%d", &no);
                push(no);
                break;
            case 2:
                no = pop();
                if (no != -999)
                    printf("\nPopped: %d", no);
                break;
            case 3:
                show();
                break;
            case 0:
                printf("\nExiting...");
                break;
            default:
                printf("\nInvalid choice");
        }
    } while (ch != 0);
}

How the Stack Implementation Works

1. Push Operation: Adds a new element to the top of the stack. If the stack is full, an overflow message is displayed.
2. Pop Operation: Removes and returns the top element from the stack. If the stack is empty, an underflow message is displayed.
3. Show Operation: Displays all elements in the stack starting from the top.

Advantages of Using a Stack

1. Simplifies Function Calls: Stacks help manage recursive function calls by storing return addresses.
2. Efficient Memory Use: Since the stack grows and shrinks dynamically, memory allocation is efficient.
3. Easy to Implement: Stacks can be easily implemented using arrays or linked lists.

Applications of Stacks

• Expression Evaluation: Stacks are used to evaluate postfix and prefix expressions.
• Undo/Redo Functionality: In text editors, stacks store the undo/redo operations.
• Parsing in Compilers: Compilers use stacks for syntax parsing.
• Balancing Parentheses: Stacks can be used to check if parentheses in an expression are balanced.

Conclusion

In this article, we've explored the stack data structure, its primary operations, and a simple stack implementation in C. Stacks are vital for developers, especially when solving problems like expression evaluation, backtracking, or recursive function management. By mastering stacks, you'll strengthen your foundation in data structures and algorithms.

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