C programmers commonly make errors regarding the precedence rules of C operators due to the nonintuitively low precedence levels of "&", "|", "^", "<<", and ">>". For example, the following C expression, intended to test the least significant bit of x
x & 1 == 0
is parsed as
x & (1 == 0)
which the compiler would probably evaluate at compile time to
(x & 0)
and then to 0.
Mistakes regarding precedence rules can be avoided by the suitable use of parentheses. Using parentheses defensively reduces errors and, if not taken to excess, makes the code more readable.
References
- ISO/IEC 9899-1999 6.5, "Expressions"
- NASA-GB-1740.13 6.4.3, "C Language"