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I am trying to write a program that takes an integer value (n) from the user then invokes my catalan numbers method and finds the nth value. It all works aside from two errors; firstly when I type in 'quit' it gives the error message 'Exception in thread "main" java.lang.NumberFormatException: For input string: "quit"'. And secondly the output keeps on repeating the nth value of the first value of n i put in along with the answer for the new value of n. I am fairly sure this is because of the line 'System.out.println(i)' however I do not know how to fix it so it only shows the answer to the current value of n.

Here is my code:

public class Exercise_3 {
    public static long catalan(int n) throws IllegalArgumentException {

        int res = 0;

        // Base case
        if (n <= 1) {
            return 1;


        }

        for (int i = 0; i < n; i++) {
            res += catalan(i) * catalan(n - i - 1);

        }
        return res;

    }

    public static void exercise3a() {
        Scanner scan = new Scanner(System.in);

        System.out.println("Please enter an integer greater than 0 and less than 30 or type 'quit' to exit :");

        String input = scan.next();
        int number = Integer.parseInt(input);

        if (input.equals("quit")) {
                System.out.println("quitting");
        }

        while (!input.equals("quit")){
                int i = (int) catalan(number);
                System.out.println(i);
                System.out.println("Please enter an integer greater than 0 and less than 30 or type 'quit' to exit :");
                String continued;
            continued = scan.next();
            int continue_loop = Integer.parseInt(continued);
                int f = (int) catalan(continue_loop);
                System.out.println(f);
            }

        }

    public static void main(String[] args) {
        exercise3a();
    }
}

Any help would be greatly appreciated.

Guy Coder
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Shaun
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  • Hint: Check your while loop and where you are checking for your exit condition. – gregwhitaker Apr 23 '17 at 15:30
  • @gregwhitaker I have tried moving the position of the 'if (input.equals("quit"))' statement but that doesn't seem to make a difference, any more clues? – Shaun Apr 23 '17 at 15:39
  • Hint: Is "input" the only variable you should be checking for the quit command? – gregwhitaker Apr 23 '17 at 15:43
  • Honestly, I don't know. I am very new to Java so an explanation of where I've messed up would be greatly appreciated – Shaun Apr 23 '17 at 15:50

1 Answers1

0

Problem is here

   String input = scan.next();
    int number = Integer.parseInt(input);

    if (input.equals("quit")) {
            System.out.println("quitting");
    }
Vasyl Lyashkevych
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