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Thread: Dividing inside a for loop. Lolwtf?

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    Default Dividing inside a for loop. Lolwtf?

    I have a for loop which looks like so: for(int x = 0; x<=1000; x++){ System.out.println(x/3); }

    Now for some insanely strange reason, when I run the code, it repeats the awnsers however many times im dividing by. So lets say its 3 it prints 000 111 222 and so on, 4 is like 1111 2222 3333 and etc. How in the world do I fix this, i've tried a bunch of different ideas, nothing.


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    Default Re: Dividing inside a for loop. Lolwtf?

    You're using integer division, which truncates the results to an integer. You want to promote the expression type to floating point.

    System.out.println(x / 3.); // note the . after the 3
    System.out.println((double) x / 3); // same result, explicitly cast x to double and 3 gets implicitly promoted

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    Default Re: Dividing inside a for loop. Lolwtf?

    for(int x = 0; x <= 1000; x++) { 
        System.out.println(x/3); 
    }

    Sorry your code is much easier to read this way. Helloworld hit the nail on the head.

    But in more detailed wording, because you are dividing x (an integer) by 3 (an integer also), your answer is going to be... you guessed it, and integer. To truncate a value is to basically shorten a number by dropping a digit(s).

    In your code, when you print out x / 3, it's going to print the truncated integer from the expression x / 3 because the type Int can't hold floating point values.

    So as helloworld said you need to cast your output to a float point, and you can do that by adding a period after 3, or casting the entire expression to a double.

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    Default Re: Dividing inside a for loop. Lolwtf?

    Quote Originally Posted by helloworld922 View Post
    You're using integer division, which truncates the results to an integer. You want to promote the expression type to floating point.

    System.out.println(x / 3.); // note the . after the 3
    System.out.println((double) x / 3); // same result, explicitly cast x to double and 3 gets implicitly promoted
    Thanks a bunch. Now my next question, i'm asking this because i'm doing the project euler first problem, and I am COMPLETLY mind boggled at the awnser. It asks what is the sum of the multiples of 3 or 5, under 1000.

    so thats 3+6+9 until the multiple is right under 1000 (995 and 999) I added all these up, and the awnser doesn't equal the awnser on project euler. What am I doing wrong? It makes me feel like they are the ones who are incorrect.

    This is my code:

    package sumsof3sand5s;
     
    public class app {
    public static int a;
    	public static  int x;
    	public static int b;
    	public static int c;
     
    	public static void main(String[] args) throws InterruptedException {
     
    		for(x = 0;x<1000;x++){
    			if(x%3==0){
    				a=a+x;
    				System.out.println(x);
    			}
    		}
     
    		Thread.sleep(2000);
    		System.out.println("");
    		for(int z = 0;z<1000;z++){
    			if(z%5==0){
    				b=b+z;
    				System.out.println(z);
    			}
    		}
     
     
    		System.out.println(a+b);
     
     
    	}

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    Default Re: Dividing inside a for loop. Lolwtf?

    Quote Originally Posted by samy109 View Post
    so thats 3+6+9 until the multiple is right under 1000 (995 and 999) I added all these up, and the awnser doesn't equal the awnser on project euler. What am I doing wrong? It makes me feel like they are the ones who are incorrect.
    Post your progress and I will be able to assist you, but we must locate the problem.

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    Default Re: Dividing inside a for loop. Lolwtf?

    Quote Originally Posted by AlexHail View Post
    Post your progress and I will be able to assist you, but we must locate the problem.
    This is my code:

    package sumsof3sand5s;
     
    public class app {
    public static int a;
    	public static  int x;
    	public static int b;
    	public static int c;
     
    	public static void main(String[] args) throws InterruptedException {
     
    		for(x = 0;x<1000;x++){
    			if(x%3==0){
    				a=a+x;
    				System.out.println(x);
    			}
    		}
     
    		Thread.sleep(2000);
    		System.out.println("");
    		for(int z = 0;z<1000;z++){
    			if(z%5==0){
    				b=b+z;
    				System.out.println(z);
    			}
    		}
     
     
    		System.out.println(a+b);
     
     
    	}


    What it does, is first it counts up the numbers 3, 6 - till 999, then gets the sum of all those numbers (166833). then it does the same for 5. 5-10, all the way to 995 (99500). Then it adds these two values up (266333). I do not see how this could be incorrect, as it does exactly what's asked.

    --- Update ---

    Nevermind I figured it out.

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    Default Re: Dividing inside a for loop. Lolwtf?

    You must compensate for those numbers that are counted twice.

    Ex. 30 is a multiple of 3, and 5. So when determining if the iteration is a multiple of either 3 or 5, it will add that number to the sum twice.

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