while & do-while loop with users decision to run program again

Question

I have a problem with my restaurant assignment - I'm required to

1. Create a while loop with a required quantity that user purchases to be between 1 and 15. User has 3 attempts and if after the third time he doesn't put the right quantity 1

2. Using a do- while loop user has to answer if he wants to run a program again. If he answers 'Y' (for yes) it runs again, if the answer is 'N' (for no ) it terminates.

I keep getting errors: the while loop does only 2 attempts, and the do while doesn't work at all.

    import java.text.DecimalFormat;
    import java.util.Scanner;

    public class newone {
       public static void main (String[] args){
         char repeat;             
         // To hold 'y' or 'n'      
         String input;      

        DecimalFormat df = new DecimalFormat("$0.00");
        //to use: df.format(doubleVariable)

        //Display any welcome message at the top of the output screen
        System.out.println("Welcome!");

        double price = 5.0;
        System.out.println("Burger is " + df.format(price));

        Scanner keyboard = new Scanner(System.in); 

            int attempts = 0;
            int maxAttempts = 3;
            int quantity;

            System.out.print("Enter amount of burgers: ");

            quantity = keyboard.nextInt();
        //LESS THAN OR EQUAL TO 3... 
        while(quantity <1 || quantity >=15 && attempts<=maxAttempts){

            if(quantity < 1 || quantity >= 15){

                System.out.println("That is an invalid amount, please try  again");
                    quantity= keyboard.nextInt();
                    ++attempts;
                    }
                    else if(quantity>1 && quantity<15){

                //user entered a valid amount  
                System.out.println("The amount is valid. You ordered: "+ quantity);
                double subTotal = quantity * price;
            }

            while (attempts>=maxAttempts){
                System.out.println("Too many attempts, you can't order");
                break;
                }
            }

         do{ 
     System.out.println("Would you like to run the program again?");        
     System.out.print("Enter Y for yes or N for no: "); 
     input = keyboard.nextLine();    // Read a line.     
     repeat = input.charAt(0);       // Get the first char.   
     } 
//it gives me an error Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0
    at java.lang.String.charAt(Unknown Source)

     while (repeat == 'Y' || repeat == 'y'); 



            }
        }}

Answer 1

Below line causes the error:

repeat = input.charAt(0);

Perhaps user is not providing any inputs (i.e. user just hits enter when program asks for any input) and hence, string doesn't have any character. Extracting first character from blank string throws this error.

The solution will be to check for empty string (using length() method) before executing charAt(0).

Answer 2

You have lots of problems here.

Here's how I'd do it. It's never too early to learn about decomposition and writing clean, readable code:

/**
 * Created by Michael
 * Creation date 3/4/2016.
 * @link https://stackoverflow.com/questions/35806509/java-while-do-while-loop-with-users-decision-to-run-program-again/35806638?noredirect=1#comment59284245_35806638
 */

import java.text.NumberFormat;
import java.util.Scanner;

public class BurgerKing {

    public static final int MAX_ATTEMPTS = 3;
    public static final int MIN_QUANTITY = 1;
    public static final int MAX_QUANTITY = 15;
    public static final NumberFormat PRICE_FORMAT = NumberFormat.getCurrencyInstance();

    public static void main (String[] args){

        Scanner keyboard = new Scanner(System.in);
        String answer;
        do {
            System.out.println("Welcome!  Please place your order");
            int quantity = getBurgerQuantity(keyboard);
            double price = getBurgerPrice(keyboard);
            System.out.println(String.format("Your total is: %s", PRICE_FORMAT.format(quantity*price)));
            System.out.print("Another order? [Y/N]: ");
            answer = keyboard.nextLine();
        } while ("Y".equalsIgnoreCase(answer));
    }

    public static boolean isValidQuantity(int quantity) {
        return (quantity >= MIN_QUANTITY && quantity =< MAX_QUANTITY);
    }

    public static int getBurgerQuantity(Scanner scanner) {
        int numBurgers;
        int attempts = 0;
        do {
            System.out.print("How many burgers would you like? ");
            numBurgers = Integer.parseInt(scanner.nextLine());
        } while (!isValidQuantity(numBurgers) && (++attempts < MAX_ATTEMPTS));
        if (attempts == MAX_ATTEMPTS) throw new IllegalArgumentException(String.format("%d attempts is too many", attempts));
        return numBurgers;
    }

    public static double getBurgerPrice(Scanner scanner) {
        String price;
        System.out.print("Name your burger price: ");
        price = scanner.nextLine();
        return Double.parseDouble(price);
    }
}