Some operators are assumed to be associative and commutative (^ is one of them). The compiler is permitted to evaluate in any order it sees fit, which if for whatever reason it decided not to evaluate right to left would give a different result than what you expect.

The compiler will, or should, generate a warning message that the result is undefined, though most will evaluate the operations in the order you'd expect.

Some things in C are defined as "implementation dependent" and can bite you if you're not aware of them.