Java Menu Driven Programming and Loops

Question

I am creating a basic program that allows users to purchase seats on a plane. I need help modifying this code so that I can return from the inner menu to the outer:

boolean done = false;
while(!done)
        System.out.println("Enter 1 to buy seat.");
        ...
        //other menu options
        ...
        System.out.println("Enter o to exit.");
        input = keyboard.nextInt();

        if (input == 0)
            done = true;

        if (input == 1)
        {
             String seat;
             System.out.println("Please enter the seat you wish to buy or enter X " +
                                "to return to the first menu.");
             seat = keyboard.nextLine();
        }

Answer 1

Some psuedo code to illustrate the idea of nesting calls as suggested by MeBigFatGuy and Senthil.

function outer() {
   print menu options
   for(;;) {
      read input
      if input == value for option 1 {
         runOption1Menu();
      }
      else if input == value for option 2 {
         runOption2Menu();
      }
      //and so on 
      else if input == value to exit this menu level {
          return;
      }
   }

This code structure can be used to nest as many levels as needed.

Answer 2

//Importing Resources (Random)
import java.util.Random;

//Importing Resources (Scanner)
import java.util.Scanner;

public class Assignment2 {

    /**
     * Scanner used for input within program
     */
    public static Scanner scanner = new Scanner(System.in);

    /**
     * Main method that provides user with a menu in which each number
     * represents a different method (e.g addtion) that they can carry out
     */
    public static void main(String[] args) {

        try {
            // Declare variable for user's option and defaulting to 0
            int menuOption = 0;
            do {
                // Setting menuOption equal to return value from showMenu();
                menuOption = showMenu();

                // Switching on the value given from user
                switch (menuOption) {

                case 1:
                    add();
                    break;
                case 2:
                    subtract();
                    break;
                case 3:
                    guessRandomNumber();
                    break;
                case 4:
                    printLoop();
                    break;
                case 5:
                    System.out.println("Quitting Program...");
                    break;
                default:
                    System.out.println("Sorry, please enter valid Option");

                }// End of switch statement

            } while (menuOption != 5);

            // Exiting message when user decides to quit Program
            System.out.println("Thanks for using this Program...");

        } catch (Exception ex) {
            // Error Message
            System.out.println("Sorry problem occured within Program");
            // flushing scanner
            scanner.next();
        } finally {
            // Ensuring that scanner will always be closed and cleaning up
            // resources
            scanner.close();
        }

    }// End of main Method

    /**
     * Method that prints menu to screen and gets returns user's option from menu
     * @return Returns user Option
     */
    public static int showMenu() {

        // Declaring var for user option and defaulting to 0
        int option = 0;

        // Printing menu to screen
        System.out.println("Menu:");
        System.out.println("1.Add");
        System.out.println("2.Subtract");
        System.out.println("3.Guess a Random Number");
        System.out.println("4. Print many times");
        System.out.println("5. Quit Program");

        // Getting user option from above menu
        System.out.println("Enter Option from above...");
        option = scanner.nextInt();

        return option;

    }// End of showMenu

    /**
     * Method that adds two random numbers (from 1-100) and take a user guess
     * for the addition.Then outputs certain statements dependent if user guess
     * is correct or not.
     */
    public static void add() {

        // Setting up new random
        Random random = new Random();

        // Declaring Integers
        int num1;
        int num2;
        int result;
        int input;
        //defaulting input to 0
        input = 0;
        // Declaring boolean for valid user answer (Defaulted to false)
        boolean validAnswer = false;
        //Declaring boolean for correct user answer (default to false)
        boolean correctAnswer=false;
        do {
            // Create two random numbers between 1 and 100
            num1 = random.nextInt(100);
            num1++;
            num2 = random.nextInt(100);
            num2++;

            //Do while loop that loops until user gives valid input
            do {
                //validAnswer set to true to avoid infinite loop
                validAnswer = true;
                // Displaying numbers for user and getting user input for answer
                System.out.println("Adding numbers...");
                System.out.printf("What is: %d + %d? Please enter answer below", num1,num2);
                result = num1 + num2;
                try {
                    input = scanner.nextInt();
                } catch (Exception ex) {
                    // Print error message
                    System.out.println("Sorry, Invalid entry for Addition...Please Retry!");
                    // flush scanner
                    scanner.next();
                    validAnswer = false;
                }
            } while (!validAnswer);

            // Line break for code clarity
            System.out.println();

            // if else statement to determine if answer is correct
            if (result == input) {

                System.out.println("Well done, you guessed corectly!");
                correctAnswer = true;
            } else {

                System.out
                        .println("Sorry incorrect, Please guess another Addition");
                correctAnswer = false;
            }
        } while (!correctAnswer);

    }// End of add

    /**
     * Method that subtracts two random numbers (from 1-100) and takes a user
     * guess for the subtraction. Then outputs certain statements dependent if
     * user guess is correct or not.
     */
    public static void subtract() {

        // Setting up random
        Random random = new Random();

        // Declaring Integers
        int num1;
        int num2;
        int result;
        int input;
        //set input to 0
        input = 0;
        // Declaring boolean for validity of userAnswer (Defaulted to false)
        boolean validAnswer = false;
        //Declaring boolean for correct user answer (default to false)
        boolean correctAnswer=false;
        do {
            // Create two random numbers between 1 and 100
            num1 = random.nextInt(100);
            num1++;
            num2 = random.nextInt(100);
            num2++;

            do {
                // Set correctAnwer to true to avoid infinite iterations
                validAnswer = true;
                // Displaying numbers for user and getting user input for answer
                System.out.println("Subtracting numbers...");
                System.out.printf("What is: %d - %d? Please enter answer below", num1,num2);
                result = num1 - num2;

                try {
                    input = scanner.nextInt();
                } catch (Exception ex) {
                    // Print error message
                    System.out.println("Sorry, Invalid entry entry for subtraction...Please retry!");
                    // flush scanner
                    scanner.next();
                    validAnswer = false;
                }
            } while (!validAnswer);

            // Line break for code clarity
            System.out.println();

            // if else statement to determine if answer is correct
            if (result == input) {

                System.out.println("Well done, you guessed corectly!");
                correctAnswer = true;
            } else {

                System.out.println("Sorry incorrect, Please attempt another subtraction");
                correctAnswer = false;
            }
        } while (!correctAnswer);

    }// end of subtract

    /**
     * A method that generates a random number between 1 and 10
     * @return randomNumber (Returns random number between 1 and 10 inclusive)
     */
    public static int generateRandomNumber() {

        //setting up random
        Random random = new Random();
        // Declaring int for random number and defaulting to 0
        int randomNumber = 0;
        // Assigning randomNumber between 1 and 10
        randomNumber = random.nextInt(10);
        randomNumber++;
        //Trace code, Remember to take out!
        System.out.println("Trace: Random no is:" + randomNumber);
        return randomNumber;

    }// end of generateRandomNumber

    /**
     * Method that allows user to guess a random number between a set range. A
     * message will then be displayed on screen to let them know if they were
     * correct or not.
     */
    public static void guessRandomNumber() {

        // declare var for user guess and default to zero
        int userGuess = 0;
        // declare boolean relating to if number is valid
        boolean validNumber = false;
        // declare boolean relating to if guess is correct
        boolean correctGuess = false;
        // declaring int equal to return value from generateRandomNumber();
        int secretNumber = generateRandomNumber();

        //Do while loop that runs until user guesses correctly
        do {

            //Do while loop that runs until a valid entry is given (i.e. int)
            do {
                try {
                    //do while loop ensuring that user guess is between 1 and 10
                    do {
                        // Get user guess (between 1 and 10)
                        System.out.println("Please enter a number between 1 and 10...");
                        userGuess = scanner.nextInt();
                        if (userGuess < 1 || userGuess > 10) {
                            validNumber = false;
                            System.out.println("Please Ensure number is between 1 and 10");
                        }else {
                            validNumber=true;
                        }
                    } while (!validNumber);
                } catch (Exception ex) {
                    //Print error message
                    System.out.println("Sorry invalid entry...");
                    // Flush scanner
                    scanner.next();
                    validNumber = false;
                }
            } while (!validNumber);

            //If else statement that outputs a message informing user if guess correct
            if (userGuess == secretNumber) {

                System.out.println("Guess correct, well done!");
                correctGuess = true;

            } else {

                System.out.println("Sorry guess Incorrect please try again!");
                correctGuess = false;
            }
        } while (!correctGuess);
    }// end ofGuessRandomNumber


    /**
     * Method that allows user to enter a string they want and print it a
     * certain no of times
     */
    public static void printLoop() {
        // Declaring and initialising Variables
        int noOfTimes = 0;
        String print = null;

        try {
            System.out.println("Please enter what you would like to print");
            print = scanner.next();
        } catch (Exception ex) {
            //error message
            System.out.println("Please give a Valid Entry...");
            // flush scanner
            scanner.next();
        }

        System.out.println("Please enter how many times you wish to print...");
        noOfTimes = scanner.nextInt();

        for (int counter = 0; counter < noOfTimes; counter++) {

            System.out.println(print);
        }
    }// End of printLoop

}// End of class