We consider a general class of systems subject to two types of uncerta
inty: A continuous deterministic uncertainty that affects the system d
ynamics, and a discrete stochastic uncertainty that leads to jumps in
the system structure at random times, with the latter described by a c
ontinuous-time finite state Markov chain. When only sampled values of
the system state is available to the controller, along with perfect me
asurements on the state of the Markov chain, we obtain a characterizat
ion of minimax controllers, which involves the solutions of two finite
sets of coupled PDEs, and a finite dimensional compensator. For the l
inear-quadratic case, a complete characterization is given in terms of
coupled generalized Riccati equations, which also provides the soluti
on to a particular H-infinity optimal control problem with randomly sw
itching system structure and sampled state measurements.