cosme

import java.util.*;
public class Stack_Backstrom
{
	static int a[] = new int [50];
	static int top = -1;
	public static void main (String args[])
	{
		Scanner scanner = new Scanner(System.in);
		System.out.println("This program performs various stack operations.");
		while(true)
		{
			System.out.println("Please select one of the numbers below:");
			System.out.println("1.Clear - Clears the contents of the stack.");
			System.out.println("2.IsEmpty - Returns true if the stack is empty, false if it is not.");
			System.out.println("3.IsFull - Returns true if the stack is full, false if it is not.");
			System.out.println("4.Push - Adds an item to the top of the stack.");
			System.out.println("5.Pop - Removes an item from the top of the stack.");
			System.out.println("6.Peek - Returns the value at the top of the stack.");
			System.out.println("7.Exit - Exits the program.");
			int Choice = scanner.nextInt();

			switch(Choice)
			{
				case 1:
				top = -1;
				break;
				case 2:
				isempty();
				break;
				case 3:
				isfull();
				break;
				case 4:
				push();
				break;
				case 5:
				pop();
				break;
				case 6:
				peek();
				break;
				case 7:
				System.exit(0);
				break;
			}
		}
	}

	static void isempty()
	{
		if (top == -1)
			System.out.println("true");
		else System.out.println("false");
	}

	static void isfull()
	{
		if(top == 50)
			System.out.println("true");
		else System.out.println("false");
	}

	static void push()
	{
		if(top == 50)
			System.out.println("Error: Stack is full.");
		else
		{
			top++;
			System.out.println("Please enter the value to be added to the top of the stack:");
			Scanner scanner = new Scanner(System.in);
			int pushval = scanner.nextInt();
			a[top] = pushval;
		}
	}

	static void pop()
	{
		if(top == -1)
			System.out.println("Error: Stack is empty.");
		else
		{
			int popval = a[top];
			top--;
			System.out.println("Value" + " " + popval + " " + "has been popped.");
		}
	}

	static void peek()
	{
		if(top == -1)
			System.out.println("Error: Stack is empty.");
		else
		{
			System.out.println("The value on top of the stack is:" + a[top]);
		}
	}
}