Stack Data Structure in C (Complete Guide with Examples)

This tutorial explains the Stack data structure in C, a Last-In-First-Out (LIFO) structure. It covers concepts, operations (push, pop, peek), array and linked list implementations, and practical examples to improve problem-solving skills.

1. What is a Stack

  1. A stack is a linear data structure that follows LIFO (Last-In-First-Out) principle
  2. Last element inserted is the first one to be removed
  3. Common examples: browser history, undo feature, function call stack

2. Stack Operations

OperationDescription
push()Insert element at top of stack
pop()Remove element from top of stack
peek()Get top element without removing
isEmpty()Check if stack is empty
isFull()Check if stack is full (for array implementation)

3. Stack Implementation Using Array


#include <stdio.h>
#define MAX 5

int stack[MAX];
int top = -1;

void push(int x) {
if(top == MAX - 1) {
printf("Stack Overflow\n");
} else {
stack[++top] = x;
printf("%d pushed to stack\n", x);
}
}

void pop() {
if(top == -1) {
printf("Stack Underflow\n");
} else {
printf("%d popped from stack\n", stack[top--]);
}
}

void peek() {
if(top == -1) {
printf("Stack is empty\n");
} else {
printf("Top element: %d\n", stack[top]);
}
}

int main() {
push(10);
push(20);
push(30);

peek();
pop();
peek();

return 0;
}

Sample Output:


10 pushed to stack
20 pushed to stack
30 pushed to stack
Top element: 30
30 popped from stack
Top element: 20

4. Stack Implementation Using Linked List


#include <stdio.h>
#include <stdlib.h>

struct Node {
int data;
struct Node *next;
};

struct Node *top = NULL;

void push(int x) {
struct Node *newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = x;
newNode->next = top;
top = newNode;
printf("%d pushed to stack\n", x);
}

void pop() {
if(top == NULL) {
printf("Stack Underflow\n");
return;
}
struct Node *temp = top;
top = top->next;
printf("%d popped from stack\n", temp->data);
free(temp);
}

void peek() {
if(top == NULL) {
printf("Stack is empty\n");
} else {
printf("Top element: %d\n", top->data);
}
}

int main() {
push(10);
push(20);
push(30);

peek();
pop();
peek();

return 0;
}

Sample Output:


10 pushed to stack
20 pushed to stack
30 pushed to stack
Top element: 30
30 popped from stack
Top element: 20

5. Key Points to Remember

  1. Stack follows LIFO principle
  2. Can be implemented using arrays or linked lists
  3. Operations: push, pop, peek, isEmpty, isFull
  4. Array-based stack has fixed size, linked-list stack is dynamic
  5. Useful in function calls, recursion, expression evaluation, undo mechanisms