Speaking generally, there are always three issues:
Operator precedence: In algebra, 1 + 2 * 3 is always 7, not 6.
Bitwise operators: Does, say, "&&" mean "logical and" or "bitwise and?" Is 7 && 16 ... true, or integer 0?
Short-circuiting: The computer stops evaluating a logical expression that is joined by "and" and "or" operators as soon as possible. If you are counting on "side effects" from the entire expression, some of them might not happen.