How much trust can I put in a standard computer running windows? To what certainty can I be sure it will run my code the way I wrote it? How can I be sure that if I declare something like "int j = 5;", j will alway be 5? Is there a way to measure trust in a standard x86 computer system? What kind of protections are there to make sure that j = 5?

I'm thinking about critical systems where nothing can be off even by one bit and everything must run exactly the way it was written to run.