[previous] MISRA-C:2004  Rule  12.5:  (Required) [next] The operands of a logical && or || shall be primary-expressions.
'Primary expressions' are defined in ISO/IEC 9899:1990 [2], section 6.3.1. Essentially they are either a single identifier, or a constant, or a parenthesised expression. The effect of this rule is to require that if an operand is other than a single identifier or constant then it must be parenthesised. Parentheses are important in this situation both for readability of code and for ensuring that the behaviour is as the programmer intended. Where an expression consists of either a sequence of only logical && or a sequence of only logical ||, extra parentheses are not required.

For example write: 

if ( ( x == 0 ) && ishigh )   /* make x == 0 primary                  */
if ( x || y || z )            /* exception allowed, if x, y and z are
                                 Boolean                              */
if ( x || ( y && z ) )        /* make y && z primary                  */
if ( x && ( !y ) )            /* make !y primary                      */
if ( ( is_odd ( y ) ) && x )  /* make call primary                    */

Where an expression consists of either a sequence of only logical && or a sequence of only logical ||, extra parentheses are not required. 

if ( ( x > c1 ) && ( y > c2 ) && ( z > c3 ) )      /* Compliant       */
if ( ( x > c1 ) && ( y > c2 ) || ( z > c3 ) )      /* not compliant   */
if ( ( x > c1 ) && ( ( y > c2 ) || ( z > c3 ) ) )  /* Compliant
                                                        extra () used */

Note that this rule is a special case of Guideline .

QAC messages that encompass this guideline:

3398 Extra parentheses recommended. A function call, array subscript, or member operation is the operand of a logical && or ||.
3399 Extra parentheses recommended. A unary operation is the operand of a logical && or ||.
3400 Extra parentheses recommended. A binary operation is the operand of a logical && or ||.


(c) The Motor Industry Research Association, 2004
QA C Source Code Analyser 8.1.2
MISRA-C:2004 Compliance Module 3.2
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