Question

Hi i want to round double numbers like this (away from zero) in C++:

  4.2 ---->   5
  5.7 ---->   6
 -7.8 ---->  -8
-34.2 ----> -35

What is the efficient way to do this?

Answer 1

inline double myround(double x)
{
  return x < 0 ? floor(x) : ceil(x);
}

As mentioned in the article Huppie cites, this is best expressed as a template that works across all float types

See http://en.cppreference.com/w/cpp/numeric/math/floor and http://en.cppreference.com/w/cpp/numeric/math/floor

or, thanks to Pax, a non-function version:

x = (x < 0) ? floor(x) : ceil(x);