Stack

import java.util.Scanner;

class Stack {
    int[] stack;
    int top;
    int size;

    Stack(int size) {
        this.size = size;
        stack = new int[size];
        top = -1; // means stack is empty
    }

    // PUSH operation
    void push(int value) {
        if (top == size - 1) {
            System.out.println("Stack Overflow! Cannot push " + value);
            return;
        }
        stack[++top] = value;
        System.out.println(value + " pushed to stack.");
    }

    // POP operation
    int pop() {
        if (top == -1) {
            System.out.println("Stack Underflow! No elements to pop.");
            return -1;
        }
        return stack[top--];
    }

    // PEEK operation
    int peek() {
        if (top == -1) {
            System.out.println("Stack is empty. Nothing to peek.");
            return -1;
        }
        return stack[top];
    }

    // CHECK EMPTY
    boolean isEmpty() {
        return top == -1;
    }

    // DISPLAY STACK
    void display() {
        if (top == -1) {
            System.out.println("Stack is empty!");
            return;
        }

        System.out.print("Stack elements: ");
        for (int i = top; i >= 0; i--) {
            System.out.print(stack[i] + " ");
        }
        System.out.println();
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter stack size: ");
        int size = sc.nextInt();

        Stack s = new Stack(size);

        boolean run = true;
        while (run) {
            System.out.println("STACK OPERATIONS");
            System.out.println("1. Push");
            System.out.println("2. Pop");
            System.out.println("3. Peek");
            System.out.println("4. Check if Empty");
            System.out.println("5. Display Stack");
            System.out.println("6. Exit");
            System.out.print("Choose an option: ");
            int choice = sc.nextInt();

            switch (choice) {
                case 1:
                    System.out.print("Enter value to push: ");
                    s.push(sc.nextInt());
                    break;

                case 2:
                    int popped = s.pop();
                    if (popped != -1)
                        System.out.println("Popped: " + popped);
                    break;

                case 3:
                    int topValue = s.peek();
                    if (topValue != -1)
                        System.out.println("Top element: " + topValue);
                    break;

                case 4:
                    if (s.isEmpty())
                        System.out.println("Stack is empty.");
                    else
                        System.out.println("Stack is NOT empty.");
                    break;

                case 5:
                    s.display();
                    break;

                case 6:
                    run = false;
                    break;

                default:
                    System.out.println("Invalid choice!");
            }
        }

        sc.close();
    }
}