之一 From C-FAQ Question 14.6 How do I round numbers?
http://c-faq.com/fp/round.html
The simplest and most straightforward way is with code like
(int)(x + 0.5)C's floating to integer conversion truncates (discards) the fractional part, so adding 0.5 before truncating arranges that fractions >= 0.5 will be rounded up. (This technique won't work properly for negative numbers, though, for which you could use something like (int)(x < 0 ? x - 0.5 : x + 0.5), or play around with the floor and ceil functions.)You can round to a certain precision by scaling:
(int)(x / precision + 0.5) * precision Handling negative numbers, or implementing even/odd rounding, is slightly trickier.Note that because truncation is otherwise the default, it's usually a good idea to use an explicit rounding step when converting floating-point numbers to integers. Unless you're careful, it's quite possible for a number which you thought was 8.0 to be represented internally as 7.999999 and to be truncated to 7.
之二 From 忆向Blog
http://www.hustyx.com/2010/69
之三 自我总结帖
http://blog.pfan.cn/katwood/53215.html
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