Java Loop: Why does this loop not stop as expected?

Question

I need help getting this loop to work. It may be because I don't really know how to use loops or the if statements. But I think I needed to use the If statements when it comes to receiving a free yogurt after 10.

import java.util.Scanner;

public class Foothill {
    public static void main(String args[]){
        Scanner scanner = new Scanner(System.in);
        int numPurchases, totalPurchased;
        boolean correct;
        String menu;
        numPurchases = 0;
        totalPurchased = 0;
        correct = false;
        while(!correct) 
        {
            System.out.println("Menu:");
            System.out.println("  P (Process Purchase)");
            System.out.println("  S (Shut down)");
            menu = scanner.nextLine();
            if (menu.charAt(0)=='S' || menu.charAt(0)=='s'){
                System.exit(0);
            } else if (menu.charAt(0)=='P' || menu.charAt(0)=='p'){
                continue;
            }
            System.out.println("Your choice: " + menu.charAt(0));
            System.out.println("How many yougurts would you like to buy?");
            numPurchases = scanner.nextInt();
            totalPurchased += numPurchases;
            if (totalPurchased > 0 || totalPurchased < 10){
                System.out.println("you have purchased " + totalPurchased + " yogurts");
            } else if (totalPurchased >= 10){
                System.out.println("Congradulations you have recieve a free Yogurt");
                System.out.println("Remainding yogurt credits: " + (totalPurchased-10));
            }
        }
    }
}

I don't really know how to use loops that well so that may be my problem because I have never made a loop using false and true

`if (totalPurchased > 0 || totalPurchased < 10){` - every number is greater than 0 or less than 10. You want `&&`. — user2357112 supports Monica, Feb 08 '14 at 06:10

score 0 · Answer 1 · answered Feb 08 '14 at 06:13

0

Just remove the the following statement, then the loop will work:

else if (menu.charAt(0)=='P' || menu.charAt(0)=='p'){
                continue;
            }

answered Feb 08 '14 at 06:13

Weibo Li

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score 0 · Answer 2 · answered Feb 08 '14 at 06:25

You had a number of problems with your code. Here is the solution:

import java.util.Scanner;

public class Foothill {
    public static void main(String args[]){
          Scanner scanner = new Scanner(System.in);
          int numPurchases, totalPurchased;
          boolean correct;
          String menu;
          numPurchases = 0;
          totalPurchased = 0;
          correct = false;
          while(!correct){
              System.out.println("Menu:");
              System.out.println("  P (Process Purchase)");
              System.out.println("  S (Shut down)");
              menu = scanner.next();
              if (menu.charAt(0)=='S' || menu.charAt(0)=='s'){
                System.exit(0);
              }
              else if (menu.charAt(0)=='P' || menu.charAt(0)=='p'){
                  System.out.println("Your choice: " + menu.charAt(0));
                  System.out.println("How many yougurts would you like to buy?");
                  numPurchases = scanner.nextInt();
                  totalPurchased += numPurchases;
              }

              if (totalPurchased > 0 && totalPurchased < 10){
                 System.out.println("you have purchased " + totalPurchased + " yogurts");
              }
              else if (totalPurchased >= 10){
                 System.out.println("Congradulations you have recieve a free Yogurt");
                 System.out.println("Remainding yogurt credits: " + (totalPurchased-10));

              }
          }
          scanner.close();
      }
  }

Like mentioned above, you probably need some way to break out of the while loop by setting correct to true.

Oh, also make sure you close Scanners to prevent resource leaks. Another side point, your code doesn't check for invalid input... — Alvin Bunk, Feb 08 '14 at 06:27

score 0 · Answer 3 · edited May 23 '17 at 11:49

As user2357112 has stated in the comments, the || operator is inappropriate for testing if a number is in a given range since that condition would be true for any number.

You could change the condition to use && instead but I don't know why you'd only display that message on a certain condition. You could print it at the end of each purchase and then print an extra message if the user has received a freebie.

System.out.println("you have purchased " + totalPurchased + " yogurts");

if (totalPurchased >= 10){
    System.out.println("Congradulations you have recieve a free Yogurt");
    System.out.println("Remainding yogurt credits: " + (totalPurchased-10));
}

You also need to know that Scanner#nextInt() does NOT consume the trailing new-line character from user input. Scanner#nextLine() however, trims this character from the read input. As a result you'll get a StringIndexOutOfBoundsException after making a purchase since the Scanner#nextLine() to read in the user's choice at the menu will eat up the trailing new-line character and your program will try to get the first character of an empty String.

As stated in the linked thread you can fix this by calling Scanner#nextLine() again after reading integer input to remove the new-line character from the buffer like so:

numPurchases = scanner.nextInt();
scanner.nextLine();

Java Loop: Why does this loop not stop as expected?

3 Answers3