C programmers commonly make errors regarding the precedence rules of C operators due to the nonintuitively low precedence levels of "&", "|", "^", "<<", and ">>". 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.
Non-Compliant Code 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.
Compliant Solution
To get this code to behave as expected, parentheses should be used to specify the order of operation.
(x & 1) == 0
References
[[ISO/IEC 9899-1999]] 6.5, "Expressions"
[[NASA-GB-1740.13]] 6.4.3, "C Language"
[[Dowd 06]] Chapter 6, "C Language Issues" (Precedence, pp. 287-288)