(Not sure if this is the right place to ask this question.)
Let's say I get a computer to calculate 1+1. It should give 2, obviously. Will it always give 2? Is there any possible combination of circumstances that could cause a computer to, after finishing its calculations, give a number other than 2?
To illustrate what I'm thinking of, for humans the answer is "no" because if they're (e.g.) sufficiently drunk, they might get it wrong.