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Java Forum / First Aid / February 2006Program will add but cannot get it to multiply
Hi, Just started Java and want to multiply odd numbers between 1 and 100. However, at the moment i can only get them to add. I tried replacing the + sign with the * multiplication sign but to no avail. Any suggestions? int sum = 0; for ( int number = 0; number <=100; number +=2 ) sum += number; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Sum Odd Integerts from 1 to 100", JOptionPane.INFORMATION_MESSAGE ); > Hi, > Just started Java and want to multiply odd numbers between 1 and 100. [quoted text clipped - 9 lines] > JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Sum Odd > Integerts from 1 to 100", JOptionPane.INFORMATION_MESSAGE ); Yup. Walk through the loop. Your loop starts with number = 0. Then you multiply sum by 0, resulting in sum = 0. And then you keep multiplying 0 by stuff, all of which of course results in 0.  Signaturemonique Ask smart questions, get good answers: http://www.catb.org/~esr/faqs/smart-questions.html > Hi, > Just started Java and want to multiply odd numbers between 1 and 100. [quoted text clipped - 9 lines] > JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Sum Odd > Integerts from 1 to 100", JOptionPane.INFORMATION_MESSAGE ); Your range is 0-99, not 1-100. What happens when you multiply something by zero? Dan. SignatureDaniel Dyer http://www.dandyer.co.uk >> int sum = 0; >> [quoted text clipped - 8 lines] > > Dan. Sorry your range is 0-100, but the point still stands. Initialise number to 1 instead of 0 and it should work. Dan. SignatureDaniel Dyer http://www.dandyer.co.uk Thanks, should have realised that. Replaced number=0 with number=1 and i still get an answer of 0. I still need to be able multiple them which I can't get working Thanks for helping me out with this. > Thanks, should have realised that. > Replaced number=0 with number=1 and i still get an answer of 0. I > still need to be able multiple them which I can't get working > Thanks for helping me out with this. I think Roedy identified the problem. It's going to be a very big number, bigger than can be represented even in a long, let alone an int. You will get overflow, so the answer will not be correct. The biggest factorial that can be represented in a 64-bit signed integer, such as a Java long, is 20! (20 x 19 x 18 x 17 ... x 2 x 1). The highest positive number you can store is 2^63 or about 9.22 x 10^18 (9.2 billion billion). Your number is much bigger. If you want to calculate that you will have to look into the BigInteger class. Dan. SignatureDaniel Dyer http://www.dandyer.co.uk I have tired multiplying numbers from 1 to 20 but that doesn't work for me, How can i get it to work as it will suffice. > I have tired multiplying numbers from 1 to 20 but that doesn't work for > me, How can i get it to work as it will suffice. What code do you have now? Did you change the type of sum from int to long? You will only be able to do 12! with an int. Dan. SignatureDaniel Dyer http://www.dandyer.co.uk Thanks for the help all, got it working. > int sum = 0; > > for ( int number = 0; number <=100; number +=2 ) > sum += number; you mean this/ Try it with 9 and see if your code works. You may be pleasantly surprised. A repeating multiplication is called a sum not a product. What you are doing is very similar to computing a factorial and runs into the same problem with the answers being too big. see .http://mindprod.com/jgloss/factorial.html SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. shannon wrote On 01/31/06 15:38,: > Hi, > Just started Java and want to multiply odd numbers between 1 and 100. [quoted text clipped - 9 lines] > JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Sum Odd > Integerts from 1 to 100", JOptionPane.INFORMATION_MESSAGE ); Your difficulty is related to an old schoolboy algebra problem: As quickly as you can, multiply the twenty-six factors (x-a) * (x-b) * (x-c) * ... * (x-z) and write down all the terms. Hint: The result is not a 26th-degree polynomial. SignatureEric.Sosman@sun.com > Your difficulty is related to an old schoolboy > algebra problem: As quickly as you can, multiply the [quoted text clipped - 4 lines] > and write down all the terms. Hint: The result is > not a 26th-degree polynomial. OK, I give up. What is the real answer? >> Your difficulty is related to an old schoolboy >> algebra problem: As quickly as you can, multiply the [quoted text clipped - 6 lines] > > OK, I give up. What is the real answer? Hint: Look at the third from last factor. Tom Hawtin SignatureUnemployed English Java programmer http://jroller.com/page/tackline/ On Fri, 03 Feb 2006 06:46:21 +0000, Thomas Hawtin <usenet@tackline.plus.com> wrote, quoted or indirectly quoted someone who said : >Hint: Look at the third from last factor (x - x ) SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > >> Your difficulty is related to an old schoolboy > >> algebra problem: As quickly as you can, multiply the [quoted text clipped - 8 lines] > > Hint: Look at the third from last factor. Aaarghh!! Caught me!. Thanks. :) Free MagazinesGet these publications absolutely FREE for up to 12 months. 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