There is no uninitialized variable, I explicitly initialized it to 5. And yes indeed, C could do what Rust does and define the order of evaluation for function

There is no uninitialized variable, I explicitly initialized it to 5. And yes indeed, C could do what Rust does and define the order of evaluation for function arguments. If the argument expressions are indeed side-effect-less, the compiler can always make use of the "as-if" rule and legally reorder the computation anyway, for example to alleviate register pressure.