[previous] MISRA-C:2004  Rule  13.2:  (Advisory) [next] Tests of a value against zero should be made explicit, unless the operand is effectively Boolean.
Where a data value is to be tested against zero then the test should be made explicit. The exception to this rule is when data represents a Boolean value, even though in C this will in practice be an integer. This rule is in the interests of clarity, and makes clear the distinction between integers and logical values.

For example, if x is an integer, then: 

if ( x != 0 )    /* Correct way of testing x is non-zero */
if ( y )         /* Not compliant, unless y is effectively 
                    Boolean data (e.g. a flag) */

QAC messages that encompass this guideline:

3344 Controlling expression is not an 'essentially Boolean' expression.
4528 An expression of 'essentially enum' type (%1s) is being used as the %2s operand of this logical operator (%3s).
4529 An expression of 'essentially enum' type (%1s) is being used as the first operand of this conditional operator (%2s).
4538 An expression of 'essentially signed' type (%1s) is being used as the %2s operand of this logical operator (%3s).
4539 An expression of 'essentially signed' type (%1s) is being used as the first operand of this conditional operator (%2s).
4548 A non-negative constant expression of 'essentially signed' type (%1s) is being used as the %2s operand of this logical operator (%3s).
4549 A non-negative constant expression of 'essentially signed' type (%1s) is being used as the first operand of this conditional operator (%2s).
4558 An expression of 'essentially unsigned' type (%1s) is being used as the %2s operand of this logical operator (%3s).
4559 An expression of 'essentially unsigned' type (%1s) is being used as the first operand of this conditional operator (%2s).
4568 An expression of 'essentially floating' type (%1s) is being used as the %2s operand of this logical operator (%3s).
4569 An expression of 'essentially floating' type (%1s) is being used as the first operand of this conditional operator (%2s).


(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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