#include <stdio.h>
#include <stdlib.h>
 
// Structure for a stack node
struct Node {
    int data;
    struct Node *next;
};
 
struct Node *top = NULL;  // Global pointer to the top of the stack
 
// Function to push an element onto the stack
void push(int value) {
    struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
    if (newNode == NULL) {
        printf("\nStack Overflow! Memory not allocated.\n");
        return;
    }
    newNode->data = value;
    newNode->next = top;  // Link the new node to the previous top
    top = newNode;        // Update top pointer
    printf("\n%d pushed to stack.\n", value);
}
 
// Function to pop an element from the stack
void pop() {
    if (top == NULL) {
        printf("\nStack Underflow! No elements to pop.\n");
        return;
    }
    struct Node *temp = top;
    printf("\n%d popped from stack.\n", top->data);
    top = top->next;  // Move top to next node
    free(temp);       // Free memory
}
 
// Function to display stack elements
void display() {
    if (top == NULL) {
        printf("\nStack is empty.\n");
        return;
    }
    struct Node *temp = top;
    printf("\nStack elements are:\n");
    while (temp != NULL) {
        printf("%d\n", temp->data);
        temp = temp->next;
    }
}
 
// Function to peek at the top element
void peek() {
    if (top == NULL)
        printf("\nStack is empty.\n");
    else
        printf("\nTop element is: %d\n", top->data);
}
 
// Main function
int main() {
    int choice, value;
 
    printf("=== STACK IMPLEMENTATION USING LINKED LIST ===\n");
 
    while (1) {
        printf("\nMenu:\n");
        printf("1. Push\n");
        printf("2. Pop\n");
        printf("3. Peek\n");
        printf("4. Display\n");
        printf("5. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
 
        switch (choice) {
            case 1:
                printf("Enter value to push: ");
                scanf("%d", &value);
                push(value);
                break;
            case 2:
                pop();
                break;
            case 3:
                peek();
                break;
            case 4:
                display();
                break;
            case 5:
                printf("\nExiting program.\n");
                exit(0);
            default:
                printf("\nInvalid choice! Try again.\n");
        }
    }
 
    return 0;
}