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Thread: Recursive Method to count vowel

  1. #1
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    Default Recursive Method to count vowel

    public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter a string: ");
    String word = input.nextLine();
    int i = 0, count = 0;
    checkVowel(word, i, word.length()-1, count);
    }

    public static void checkVowel(String word, int start, int last, int count) {
    if (start == last)
    {
    System.out.println("Total number of vowel is " + count);
    }
    else
    {
    if (word.charAt(start) == 'a' || word.charAt(start) == 'e' || word.charAt(start) == 'i' ||
    word.charAt(start) == 'o' || word.charAt(start) == 'u') {
    count++;
    }
    checkVowel(word, start++, last, count);
    }
    }


    this is my code, but somehow i gt "Exception in thread "main" java.lang.StackOverflowError" , can anyone help find what's the problem??


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Recursive Method to count vowel

    When posting code, please use highlight tags.

    What happened when you stepped through this with a debugger, or at least added print statements?

    Hint: What is the value of start each time the function is called?
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    Default Re: Recursive Method to count vowel

    public static void checkVowel(String word, int i, int last, int count) {
            if (i == last)
            {
                System.out.println("Total number of vowel is " + count);
            }
            else
            {  
               [B] i++;[/B]
                if (word.charAt(i) == 'a' || word.charAt(i) == 'e' || word.charAt(i) == 'i' ||
                    word.charAt(i) == 'o' || word.charAt(i) == 'u') {
                    count++;    
                }
                checkVowel(word, i, last, count);
            }           
        }

    Thx for the hints..... sorry about the highlight, will keep it in mind.......

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    Default Re: Recursive Method to count vowel

    The problem lies in the recursive function, which must return something to get the previous level where it was invoked. Pleaes try the following:
    public class RecursiveFunctionTest {

    private static final String VOWELS = "aeiouAEIOU";

    public static int checkVowels(String word, int start, int end, int count){
    if(start >= end){
    return count;
    }
    else{
    if(VOWELS.indexOf(word.charAt(start)) != -1)
    count++;
    }

    return checkVowels(word, ++start, end, count);
    }

    public static void main(String[] args){
    Scanner input = new Scanner(System.in);
    System.out.println("Enter a String: ");
    String word = input.nextLine();
    int count = 0;
    count = checkVowels(word, 0, word.length()-1, count);
    System.out.println("The total number of vowels is " + count);
    }
    }

  5. #5
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    Default Re: Recursive Method to count vowel

    No, the recursive function mustn't return a value in order to terminate. For example, this function is OK:
        public static void f(int x, int term) {
            if(x >= term) {}
            else {
                System.out.println(x + " " + term);
                f(x + 1, term);
            }
        }

    StackOverflowException means, that the function can't terminate. Let's have a look at the termination condition:
            if (i == last)
            {
                System.out.println("Total number of vowel is " + count);
            }
    The function terminates only when i == last. I suspect, that at some point you may erroneously call the function with i > last. In this case function will never terminate, because i increases from call to call. Try "i >= last" termination condition instead of "i == last".

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    Default Re: Recursive Method to count vowel

    Return a value or not does not matter for a recursive function indeed. The core part is to terminate it. So I agree with you that something is wrong with the termination condition. So in my example, I used ">=" instead.

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    Default Re: Recursive Method to count vowel

    Guys, please stop trying to do his homework for him- Gary, the advice you offered is incorrect.

    The problem lies in the parameters being passed into the recursive call. It's not helpful to simply fix the code for him. I have suggested that the OP add some print statements or step through this with a debugger to figure it out on his own, which is what he should be doing.

    OP, did you fix your problem?
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