  We study fluctuations of the number of Bose condensed atoms in weakly
interacting homogeneous and trapped gases. For a homogeneous system we apply
the particle-number-conserving formulation of the Bogoliubov theory and
calculate the condensate fluctuations within the canonical and the
microcanonical ensembles. We demonstrate that, at least in the low-temperature
regime, predictions of the particle-number-conserving and traditional,
nonconserving theory are identical, and lead to the anomalous scaling of
fluctuations. Furthermore, the microcanonical fluctuations differ from the
canonical ones by a quantity which scales normally in the number of particles,
thus predictions of both ensembles are equivalent in the thermodynamic limit.
We observe a similar behavior for a weakly interacting gas in a harmonic trap.
This is in contrast to the trapped, ideal gas, where microcanonical and
canonical fluctuations are different in the thermodynamic limit.
