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Thread: Need help with loop
 08092012, 10:18 AM #1Member
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 08092012, 10:31 AM #2
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Re: Need help with loop
If a number 'A' is the sum of the first 'n' numbers then n == (Math.sqrt(1+8*A)1)/2. Do your math.
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 08092012, 10:53 AM #3Member
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Re: Need help with loop
Thanks for the formula, it kinda takes me a while to wrap my head around the math. I tried implementing it in, but it doesn't recognise that 4 isn't an exact sum for an example. When you input 4, the (k == 0) part should take over, instead it returns 1 to 2. :/ Did I not put it in properly?
Last edited by thegreatzo; 08092012 at 01:30 PM.
 08092012, 11:08 AM #4Moderator
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Re: Need help with loop
Um, you cannot get 4 from adding numbers from 1 consecutively.
1+2 = 3
1+2+3 = 6Please do not ask for code as refusal often offends.
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 08092012, 11:23 AM #5Member
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Re: Need help with loop
Yes I know that, but the problem is the program is not recognising that. It's supposed to work out that if you can't get the sum of n by adding numbers from 1 consecutively then it returns 0 and the message "the number n is not an exact sum". How can I get it to do that?
Testing it I tried:
Type an integer:
3
The number 3 is the sum of integers from 1 to 2  this is correct
Type an integer:
4
The number 4 is the sum of integers from 1 to 2  this is incorrect
Type an integer:
5
The number 5 is the sum of integers from 1 to 2  this is incorrect
Type an integer:
6
The number 6 is the sum of integers from 1 to 3  this is correct
 08092012, 11:30 AM #6Moderator
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Re: Need help with loop
That's because Jos' formula has one important criteria you are not taking into account:
"If a number 'A' is the sum of the first 'n' numbers ..."
You will need to calculate 'n' and then do a sum to check whether it is actually correct.Please do not ask for code as refusal often offends.
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 08092012, 11:38 AM #7
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 08092012, 12:18 PM #8Member
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Re: Need help with loop
How do i do that lol?
Do you reckon an if statement for suffice for that?
something like:
If (the sum of k does not equal n) {
k = 0;
}Last edited by thegreatzo; 08092012 at 12:24 PM.
 08092012, 12:19 PM #9Moderator
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 08092012, 12:31 PM #10
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Re: Need help with loop
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 08092012, 08:04 PM #11
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Re: Need help with loop
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 08092012, 09:51 PM #12
Re: Need help with loop
I had a copy in a cached page, so here it is. Any more removal of relevant content and the member will be banned.
db
Hey there,
I've got a program which I need to test whether an integer n is the exact sum of k consecutive integer numbers starting from 1.
eg. 6 is 1 + 2 + 3 and therefore k = 3 and if I put in 4 then it returns false. But what I've only able to achieve so far is to get the program to add numbers 1 to n together, so if I enter 6 I get 21 because 1 + 2 + 3 + 4 + 5 + 6 = 21, but this isn't what I need the program to do. I'm kinda stuck, I've tried a few other things but they aren't working. How can I get the loop to increment up to n then return that last number. eg. 6 returns 3 as mentioned above.
Java Code:import java.util.Scanner; public class ExactSum { /** * @param args */ public static void main(String[] args) { Scanner keyboard = new Scanner(System.in); System.out.println("Type an integer:"); int n = keyboard.nextInt(); int k = 0; for(int i = 1;i<=n;i++) { k = k + i; } if (k == 0) { System.out.println("The number "+n+" is not an exact sum"); } else {System.out.println("The number "+n+" is the sum of integers from 1 to "+k+" "); } } }
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