#include <stdio.h>
#include <stdlib.h>
struct Node {
    int data;
    struct Node* next;
};
struct Node* top = NULL;
int isEmpty();
void push(int value);
void pop();
void peek();
void display();
int isEmpty() {
    return top == NULL;
}
void push(int value) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    if (newNode == NULL) {
        printf("Heap overflow! Cannot push %d\n", value);
        return;
    }
    newNode->data = value;
    newNode->next = top;
    top = newNode;
    printf("%d pushed to stack.\n", value);
}
void pop() {
    if (isEmpty()) {
        printf("Stack underflow! Cannot pop.\n");
    } else {
        struct Node* temp = top;
        printf("%d popped from stack.\n", top->data);
        top = top->next;
        free(temp);
    }
}
void peek() {
    if (isEmpty()) {
        printf("Stack is empty! Nothing to peek.\n");
    } else {
        printf("Top element is: %d\n", top->data);
    }
}
void display() {
    if (isEmpty()) {
        printf("Stack is empty.\n");
    } else {
        struct Node* temp = top;
        printf("Stack elements (top to bottom):\n");
        while (temp != NULL) {
            printf("%d\n", temp->data);
            temp = temp->next;
        }
    }
}
int main() {
    int choice, value;
    while (1) {
        printf("1. Push\n");
        printf("2. Pop\n");
        printf("3. Peek\n");
        printf("4. Display\n");
        printf("5. Check if Empty\n");
        printf("6. 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:
                if (isEmpty())
                    printf("Stack is empty.\n");
                else
                    printf("Stack is not empty.\n");
                break;
            case 6:
                printf("Exiting program.\n");
                exit(0);
            default:
                printf("Invalid choice. Please try again.\n");
        }
    }

    return 0;
}