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Thread: help with trace tables for loops

  1. #1
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    Default help with trace tables for loops

    For my java homework I have to provide a trace table for the following loop:

    int i = 10; int j = 0; int n = 0;
    while (i > 0) { i--; j++; n = n + i - j; }

    When I put it into eclipse I get the answer:
    i= 0
    j= 10
    n= -10

    but when I try to trace it by hand I get
    i j n i>0
    10 0 0 t
    9 1 8 t
    8 2 14 t
    7 3 18 t
    6 4 20 t
    5 5 20 t
    4 6 18 t

    and so on.... Can someone please tell me why eclipse only prints out the last line? It didn't with any of the other trace tables I was trying to check my work on


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    Default Re: help with trace tables for loops

    Please show the whole while statement and any other info you think would be helpful to answer your question.

    BTW - If your while statement is formatted in your code as it is above, add the expected white space to make it readable before bothering to post it. Most won't bother even reading code formatted as you've shown.

  3. #3
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    Default Re: help with trace tables for loops

    Sorry, that's just the way it looked in the book

       public class Practice {
     
    	public static void main(String[] args) {
     
    		int i = 10;
    		int j = 0;
    		int n = 0;
     
    		{
    			while (i > 0) {
    				i--;
    				j++;
    				n = n + i - j;
    			}
     
    		}
     
    		System.out.println(i);
    		System.out.println(j);
    		System.out.println(n);
     
    	}
    }

    eclipse just prints out:
    0
    10
    -10

    But when I do it by hand this is what my table looks like:

    i j n i>0
    10 0 0 T
    9 1 8 T
    8 2 14 T
    7 3 18 T
    6 4 20 T
    5 5 20 T
    4 6 18 T
    3 7 14 T
    2 8 8 T
    1 9 0 T
    0 10 -10 F

    (sorry ^ I can't get my table to stay formatted with spaces)

    On the other while statements I put into eclipse to check my work, it printed out the whole table, not just the last line, so I'm wondering if I'm doing something wrong?

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    Default Re: help with trace tables for loops

    Thank you. Much better.

    In order for the print commands to be executed multiple times and therefore printing multiple results, they must be inside the while loop. The fact that only one line prints should be expected from the code you've posted. (Why the extra '{ }'?)

    Then, if the 3 results are to be printed on a single line, don't use println() for the first two print statements.

    There will be other formatting cleanups to do, but if you make the above changes, you'll be on your way.

  5. The Following User Says Thank You to GregBrannon For This Useful Post:

    catisch (October 19th, 2013)

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