Well..

  C and C++ offer a wide variety of arithmetic types.
  Double precision is not required by the standards
  (except by the optional annex F of C99, covering
  IEEE 754 arithmetic), but on most systems, the
  double type corresponds to double precision.
  However, on 32-bit x86 with extended precision
  by default, some compilers may not conform to
  the C standard and/or the arithmetic may suffer
  from double-rounding issues.