How does one identify the weakest preconditions in Hoare triples, when a variable has been sampled from a uniform distribution?

Question

I am learning about Dijkstra's weakest precondition inference technique (I have a Undergraduate and Master's in Mechanical Engineering). I have understood the basics of this technique from here. I'd like to know what happens if the set of equations is stochastic in nature. Here is a minimal example that I came up with, on the fly. Could someone please tell me the preconditions for these equations -

{What's the precondition for x here}

x ~ Uniform(0,1)

{ x != -1 }

z = x + 1;

{ z != 0 }