PRECISION_OUTPUT:
  C++ version.
  Demonstrate the precision() function for controlling the default
  precision of floating point output.

  Save prec = cout.precision() = 6

  Sqrt ( 2.0 ) = 1.41421
  Sqrt ( 3.0 ) = 1.73205

  Use setprecision(16), but only on the Sqrt ( 2.0 ) statement.
  However, all floating point output will now have the new precision.

  Sqrt ( 2.0 ) = 1.414213562373095
  Sqrt ( 3.0 ) = 1.732050807568877

  Use cout.precision(10) to request 10 digits of precision.

  Sqrt ( 2.0 ) = 1.414213562
  Sqrt ( 3.0 ) = 1.732050808

  Use cout.precision(prec) to restore default precision.

  Sqrt ( 2.0 ) = 1.41421
  Sqrt ( 3.0 ) = 1.73205