Push & Pop, Array and Linked Implementation of Stack in C

 

1️⃣ Stack Using Array in C

An array-based stack uses a fixed-size array to store elements, and a top variable to track the topmost element.

📌 Structure of Stack using Array

#include <stdio.h>
#define MAX 100  // Maximum stack size

int stack[MAX];  // Array to store stack elements
int top = -1;    // Stack is empty initially

// Push operation (Insert an element)
void push(int value) {
    if (top == MAX - 1) {
        printf("Stack Overflow\n");
        return;
    }
    stack[++top] = value;
}

// Pop operation (Remove an element)
int pop() {
    if (top == -1) {
        printf("Stack Underflow\n");
        return -1;
    }
    return stack[top--];
}

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

int main() {
    push(10);
    push(20);
    push(30);
    display();
    
    printf("Popped: %d\n", pop());
    display();
    
    return 0;
}

🔹 Time Complexity:

• Push: O(1)
• Pop: O(1)
• Display: O(n)

---

2️⃣ Stack Using Linked List in C

A linked list-based stack dynamically allocates memory, so there's no size limitation. Each node contains a data value and a pointer to the next node.

📌 Structure of Stack using Linked List

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

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

// Top pointer to track stack top
struct Node* top = NULL;

// Push operation (Insert an element)
void push(int value) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    if (!newNode) {
        printf("Heap Overflow\n");
        return;
    }
    newNode->data = value;
    newNode->next = top;
    top = newNode;
}

// Pop operation (Remove an element)
int pop() {
    if (top == NULL) {
        printf("Stack Underflow\n");
        return -1;
    }
    int value = top->data;
    struct Node* temp = top;
    top = top->next;
    free(temp);
    return value;
}

// Display Stack Elements
void display() {
    if (top == NULL) {
        printf("Stack is empty\n");
        return;
    }
    struct Node* temp = top;
    printf("Stack elements: ");
    while (temp) {
        printf("%d ", temp->data);
        temp = temp->next;
    }
    printf("\n");
}

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

    printf("Popped: %d\n", pop());
    display();

    return 0;
}

🔹 Time Complexity:

• Push: O(1)
• Pop: O(1)
• Display: O(n)

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3️⃣ Key Differences: Array vs. Linked List Stack

Feature	Stack Using Array	Stack Using Linked List
Size	Fixed, pre-defined	Dynamic, no limit
Memory Usage	Uses contiguous memory	Uses extra memory for pointers
Insertion/Deletion	O(1) but size limited	O(1) and dynamic
Overflow Risk	Yes (if array is full)	No (unless heap is full)
Underflow Risk	Yes (if stack is empty)	Yes (if stack is empty)