  We predict two topological phase transitions for cadmium arsenide
(\ce{Cd3As2}) thin films under in-plane magnetic field, taking advantage of a
four-band $k\cdot p$ model and effective $g$ factors calculated from first
principles. Film thickness, growth direction and in-plane Zeeman coupling
strength can all serve as control parameters to drive these phase transitions.
For (001) oriented \ce{Cd3As2} thin films, a two dimensional Weyl semimetal
phase protected by $C_{2z}\mathcal{T}$ symmetry can be realized using an
in-plane magnetic field, which has recently been reported in our companion
paper. We then put forth two pathways to achieve in-plane anomalous Hall
effects (IPAHE). By either introducing a trigonal warping term or altering the
growth orientation, the emergent $C_{2z} \mathcal{T}$ symmetry can be broken.
Consequently, in the clean limit and at low temperatures, quantized Hall
plateaus induced by in-plane Zeeman fields become observable.
