C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  HOW TO: round float numbers?          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Nobody Guest Posted: Mon Sep 27, 2004 6:59 am    Post subject: HOW TO: round float numbers? How does one round a float? ie... 4.4 returns 4, while 4.5 returns 5. I see the floor and ceiling functions, but that floor would take 4.4 and return 4 and ceiling would return 5. I guess I could find the part after the decimal, but there doesn't seem to be a way to do that either. Other then subtracting the floor and multiplying by 10 and taking the floor of that and checking if its 5 or higher, but that seems really lame. There has to be a better way. Back to top ES Kim Guest Posted: Mon Sep 27, 2004 7:06 am    Post subject: Re: HOW TO: round float numbers? "Nobody" <nobody (AT) cox (DOT) net> wrote Quote: How does one round a float? ie... 4.4 returns 4, while 4.5 returns 5. I see the floor and ceiling functions, but that floor would take 4.4 and return 4 and ceiling would return 5. I guess I could find the part after the decimal, but there doesn't seem to be a way to do that either. Other then subtracting the floor and multiplying by 10 and taking the floor of that and checking if its 5 or higher, but that seems really lame. There has to be a better way. Here is a simple way: you add 0.5 to the float number and floor it. float f; int i = static_cast<int>(f + 0.5); -- ES Kim Back to top John Harrison Guest Posted: Mon Sep 27, 2004 7:29 am    Post subject: Re: HOW TO: round float numbers? "ES Kim" <no (AT) spam (DOT) mail> wrote Quote: "Nobody" <nobody (AT) cox (DOT) net> wrote in message news:XSO5d.114888$yh.83871 (AT) fed1read05 (DOT) .. How does one round a float? ie... 4.4 returns 4, while 4.5 returns 5. I see the floor and ceiling functions, but that floor would take 4.4 and return 4 and ceiling would return 5. I guess I could find the part after the decimal, but there doesn't seem to be a way to do that either. Other then subtracting the floor and multiplying by 10 and taking the floor of that and checking if its 5 or higher, but that seems really lame. There has to be a better way. Here is a simple way: you add 0.5 to the float number and floor it. float f; int i = static_cast<int>(f + 0.5); But that doesn't work for negative numbers. Here's a better way inline int round(double x) { return static_cast<int>(x + x > 0.0 ? +0.5 : -0.5); } This is OK for simple use, but it doesn't check for overflow. john Back to top Vyacheslav Kononenko Guest Posted: Mon Sep 27, 2004 6:16 pm    Post subject: Re: HOW TO: round float numbers? "ES Kim" <no (AT) spam (DOT) mail> wrote Quote: "Nobody" <nobody (AT) cox (DOT) net> wrote in message news:XSO5d.114888$yh.83871 (AT) fed1read05 (DOT) .. How does one round a float? ie... 4.4 returns 4, while 4.5 returns 5. I see the floor and ceiling functions, but that floor would take 4.4 and return 4 and ceiling would return 5. I guess I could find the part after the decimal, but there doesn't seem to be a way to do that either. Other then subtracting the floor and multiplying by 10 and taking the floor of that and checking if its 5 or higher, but that seems really lame. There has to be a better way. Here is a simple way: you add 0.5 to the float number and floor it. float f; int i = static_cast<int>(f + 0.5); -- ES Kim What 4.45 should be rounded to? If 5 then you may use 0.5555555555555555 instead. Regards, Slava Back to top Howard Guest Posted: Mon Sep 27, 2004 8:28 pm    Post subject: Re: HOW TO: round float numbers? Quote: ES Kim What 4.45 should be rounded to? If 5 then you may use 0.5555555555555555 instead. Using the "conventional" method of rounding (i.e., not banker's rounding), 4.45 would round to 4, because it's less than 4.5. You don't round the last digit, then the previous one, then the previous one, etc. You simply round up for fractions greater or equal to .5. (Assuming rounding to a whole number, not to a specific decimal place, obviously.) -Howard Back to top John Harrison Guest Posted: Tue Sep 28, 2004 6:43 am    Post subject: Re: HOW TO: round float numbers? "Howard" <alicebt (AT) hotmail (DOT) com> wrote Quote: ES Kim What 4.45 should be rounded to? If 5 then you may use 0.5555555555555555 instead. Using the "conventional" method of rounding (i.e., not banker's rounding), 4.45 would round to 4, because it's less than 4.5. You don't round the last digit, then the previous one, then the previous one, etc. You simply round up for fractions greater or equal to .5. (Assuming rounding to a whole number, not to a specific decimal place, obviously.) -Howard I've never heard of banker's rounding. When is it used and why? john Back to top Howard Guest Posted: Tue Sep 28, 2004 2:40 pm    Post subject: Re: HOW TO: round float numbers? "John Harrison" <john_andronicus (AT) hotmail (DOT) com> wrote Quote: I've never heard of banker's rounding. When is it used and why? john Bankers' rounding is when you always round to the nearest even penny. So you'd round 4.5 cents to 4 cents, but 5.5 cents to 6 cents. The reason for it is because banks tend to add up a lot of (already rounded) values, and a good deal of those are half-cent values prior to rounding. Using normal rounding, the half-cent values would always round up, resulting in skewing of the final total upwards. Using bankers' rounding, the final result is much closer to the value you'd get by adding the un-rounded values (and then rounding the final result). So it's used to make their totals more accurate, basically. -Howard Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.