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

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

struct node* top = NULL;

// Push
void push(int x) {
    struct node* newnode = (struct node*)malloc(sizeof(struct node));
    if (newnode == NULL) {
        printf("Overflow\n");
        return;
    }
    newnode->data = x;
    newnode->next = top;
    top = newnode;
    printf("Pushed %d\n", x);
}

// Pop
void pop() {
    if (top == NULL) {
        printf("Underflow\n");
        return;
    }
    struct node* temp = top;
    printf("Popped %d\n", temp->data);
    top = top->next;
    free(temp);
}

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

// Main
int main() {
    int ch, x;

    do {
        printf("\n--- STACK MENU ---\n");
        printf("1.Push\n2.Pop\n3.Display\n4.Exit\n");
        printf("Enter choice: ");
        scanf("%d", &ch);

        switch (ch) {
            case 1:
                printf("Enter value: ");
                scanf("%d", &x);
                push(x);
                break;

            case 2:
                pop();
                break;

            case 3:
                display();
                break;

            case 4:
                printf("Exiting...\n");
                break;

            default:
                printf("Invalid choice!\n");
        }

    } while (ch != 4);

    return 0;
}