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Thread: Error with OR operator

  1. #1
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    Default Error with OR operator

    Hi, I know this is going to be SO simple when its pointed out but I've been working on this for the past 3 hours and I just can't understand it. I am VERY new to Java and I am trying to solve the 1st problem from project Euler. The problem is: To add all the natural numbers below 1000 that are divisable by 3 or 5. The following code determins whether the number is divisible by 3 and adds i to the total each time it finds a one. This part of the code works perfectly and I get the expected outcome. I can also change the value to 5 and that works accordingly.

    class EulerFirstProject {
    	public static void main(String[] args) {
     
    		int total = 0;
     
    		for (int i = 0; i < 1000; i++) {
    			if (i % 3 != 0) {
    				continue;
    			}
    			total += i;
    		}
     
    		System.out.println(total);
    	}
    }

    So give that this works perfectly I figured I would just be able to add an OR operator to determine whether i is divisible by 3 OR 5:

    class EulerFirstProject {
    	public static void main(String[] args) {
     
    		int total = 0;
     
    		for (int i = 0; i < 1000; i++) {
    			if ((i % 3 != 0) || (i % 5 != 0)) {
    				continue;
    			}
    			total += i;
    		}
     
    		System.out.println(total);
    	}
    }

    However for some reason this simply returns the value 49500. Witch is wrong. I have tried replacing 1000 with 10 which should give me a value of 23 but I get 0. Any pointers would be hugely appreciated.

    Thanks
    Last edited by tarkal; September 4th, 2011 at 03:03 PM.


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Error with OR operator

    To figure out how to write the conditions correctly, write a small simple program with a loop with the if test inside. Add printlns to show when the conditions are true and when they are not and to show the value of i for both those cases.

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    Default Re: Error with OR operator

    Ohhhhhhhhh, I can't beleive it... I'm so simple!!! Thanks very much for the quick feedback. I'm so sorry for such a stupid post

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Error with OR operator

    No problem. Lots of programmers have problems with != and || together.
    A quick short program to printout what is happening and the light comes on.

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