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Thread: hey guys new to recursion any ideas for me?

  1. #1
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    Exclamation hey guys new to recursion any ideas for me?

    Im supposed to Write a recursive method that computes the sum of the first n strictly positive integers. Im new to recursion any help would be great. im getting errors at moment...


    [/
    HTML Code:
    mport java.util.Scanner;
    public class SumTester
    {
    	public static void main(String[] args)
    	{
    		Scanner in = new Scanner(System.in);
    		
    		int sum = 0;		
    		System.out.println("\nPlease Enter n"); // get n from user
    		int n = in.nextInt();	
    	
    	} 
    
    	}
    		// recursively computes the sum of the first n integers
    		public static int sum(int n)
    		{
    			int sum = n;
    			if (N == 1) return 1; 
    			return N * sum(N-1); 
    			System.out.println("Recursively computing sum of the first 5 positive integers");
    			System.out.println("Sum" + n + "=" + sum);
    			//return sum;
    			}
    	
    }


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: hey guys new to recursion any ideas for me?

    Your algorithm needs a little work. Try this:

    1. See if your current number n is 1. If it is, return 1.
    2. Otherwise, sum(n) = sum(n-1) + n

  3. #3
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    Default Re: hey guys new to recursion any ideas for me?

    many thanks for the reply helloworld i have ammended it but having one error cant quiet see where im going wrong.
    HTML Code:
    import java.util.Scanner;
    public class SumTester
    {
    	public static void main(String[] args)
    	{
    		Scanner in = new Scanner(System.in);	
    		System.out.println("\nPlease Enter n"); // get n from user
    		int n = in.nextInt();			
    	}	 
    		
    		// recursively computes the sum of the first n integers
    		public static int sum(int n)
    		{
    			if (n ==1)
    				return 1;
    			else
    				return sum(n) = sum(n-1) + n;
    				
    			System.out.println("sum" + (n) + "=" + (n));
    			}
    	
    }
    Last edited by JavaNoob82; February 23rd, 2010 at 03:52 PM. Reason: wrong program sorry

  4. #4
    Senile Half-Wit Freaky Chris's Avatar
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    Default Re: hey guys new to recursion any ideas for me?

    Welcome back, Steve's got you stumped on the first question I see.

    use [code][/code] tags rather than html tags.

    Also you might wish to actually call your recursive method.
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

  5. #5
    Super Moderator helloworld922's Avatar
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    Default Re: hey guys new to recursion any ideas for me?

    Your printing out statement in sum can never be reached (can you see why?). Java's compiler recognizes this and will through an error. Put that print out statement somewhere inside your main method, and as chris said, call the method

    System.out.println("The sum is " + sum(n));

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