C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How to rid a Double of 0s after the decimal point when using          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Guest Posted: Thu Feb 23, 2006 1:06 am    Post subject: How to rid a Double of 0s after the decimal point when using If I have the following declaration: char smbuf[40]; double dValue; and execute the following statement, with smbuf being " 0.115 %": sscanf(smbuf,"%lf %%", &dValue); dValue is then assigned 0.11500000000000. Is there a way to assign 0.115 to dValue, without all those 0s after the decimal point? Thanks. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jim Langston Guest Posted: Thu Feb 23, 2006 12:06 pm    Post subject: Re: How to rid a Double of 0s after the decimal point when u <minjie (AT) excite (DOT) com> wrote in message news:1140612595.554168.9000 (AT) z14g2000cwz (DOT) googlegroups.com... Quote: If I have the following declaration: char smbuf[40]; double dValue; and execute the following statement, with smbuf being " 0.115 %": sscanf(smbuf,"%lf %%", &dValue); dValue is then assigned 0.11500000000000. Is there a way to assign 0.115 to dValue, without all those 0s after the decimal point? Thanks. dValue is assigned the value 0.115 (it may actually even be a different number depending if 0.115 can be exactly represented in a float). There are many ways to represent this value depending on how you output it. A double holds a number. For any given number there is only one way to hold that number in a numeric variable (int, char, float, double, etc..). Try this after your sscanf: std::cout << dValue << std::endl; and #include <iostream> What value do you get? I would be shown 0.115, but this could change depending on how I had my std::out formatted. If I did: std::cout << fixed; std::cout << dValue; I would get 0.115000 Show the code that's printing 0.1150000000000 and we can show you how to change it. Are you using std::cout? printf? Something else? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze Guest Posted: Thu Feb 23, 2006 3:06 pm    Post subject: Re: How to rid a Double of 0s after the decimal point when u minjie (AT) excite (DOT) com wrote: Quote: If I have the following declaration: char smbuf[40]; double dValue; and execute the following statement, with smbuf being " 0.115 %": sscanf(smbuf,"%lf %%", &dValue); dValue is then assigned 0.11500000000000. I'm pretty sure it isn't. Such a thing isn't possible on most machines -- 0.115 isn't in the set of possible values of a double. Quote: Is there a way to assign 0.115 to dValue, without all those 0s after the decimal point? dValue contains a value, not a textual representation of the value. If the conversion routins in sscanf are any good, that value is probably very, very close to (but not exactly equal) the value 0.115. How you display the value is up to you -- the default with ostream (and with printf) is in %g format with 6 digits precision. What you seem to want is %f with 3 digits precision. And I have no idea what you are actually doing, since what you are seeing isn't the default -- it corresponds to the default for Java, but must be requested explicitly in C++. At any rate, I'd say that you need to read "What Every Computer Programmer Should Know about Floating Point", by Goldberg. I don't have a link directly, but it's available at several locations on the Web -- a quick search with Google should turn up one near you. -- James Kanze GABI Software Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Francis Glassborow Guest Posted: Thu Feb 23, 2006 7:06 pm    Post subject: Re: How to rid a Double of 0s after the decimal point when u In article <1140699872.313562.286620 (AT) t39g2000cwt (DOT) googlegroups.com>, kanze <kanze@gabi-soft.fr> writes Quote: I'm pretty sure it isn't. Such a thing isn't possible on most machines -- 0.115 isn't in the set of possible values of a double. Depends how doubles are represented. C++ does not require floating point types to be represented in a binary form even if most implementations do that. -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit For project ideas and contributions: http://www.spellen.org/youcandoit/projects [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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