C Interview Questions and Answers

 

How do I round numbers?

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.

Posted by:Richards