public static void displayMenu(String input)
		{
		if(menuNumber.equals("0") && input.equals("0"))
			{
			System.out.println("Goodbye!");
			System.exit(0);
			}
		switch (input)
			{
			case "0":
				{
				System.out.println("What would you like to do?");
				System.out.println("0) exit program");
				System.out.println("1) add or delete a student\n2) change student grades/schedule\n3) sort students");
				menuNumber = "0";
				break;
				}
			//add delete student
			case "1":
				{
				System.out.println("What would you like to do?");
				System.out.println("0) return to main menu");
				System.out.println("1) add a student");
				System.out.println("2) delete a student");
				menuNumber = "1";
				break;
				}
			//change grade/class
			case "2":
				{
				System.out.println("What would you like to do?");
				System.out.println("0) return to main menu");
				System.out.println("1) change a students grade");
				System.out.println("2) change a students class");
				menuNumber = "2";
				break;
				}
			//sort by last name/grade/class
			case "3":
				{
				System.out.println("What would you like to do?");
				System.out.println("0) return to main menu");
				System.out.println("1) sort by last name");
				System.out.println("2) sort by grade");
				System.out.println("3) sort by class name");
				menuNumber = "3";
				break;
				}
			default:
				{
				System.out.println("error input not recognized");
				run();
				return;
				}
			}
		}