If the Possible Errors option is on, the compiler checks for some common typographical mistakes that are legal C syntax but that may have unwanted side effects, such as putting in unintended semicolons or confusing = and ==. The compiler generates a warning if it encounters one of these:

• An assignment in a logical expression or the condition in an if, while, or for expression. This check is useful if you frequently use = when you meant to use ==. For example:

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if (a=b) f();                  // WARNING: a=b is an assignment

if ((a=b)!=0) f();       // OK: (a=b)!=0 is a comparison, no warning

if (a==b) f();                // OK: (a==b) is a comparison, no warning

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• An equal comparison in a statement that contains a single expression. This check is useful if you frequently use == when you meant to use =. For example:

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a == 0;                // WARNING: This is a comparison.
a = 0;                  // OK: This is an assignment, no warning

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• A semicolon (;) directly after a while, if, or for statement. For example, the statement generates a warning and is probably an unintended infinite loop:

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while (i++);   // WARNING: Unintended infinite loop

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while (i++) ; // OK: White space separation, no warning
while (i++)     /*: Comment separation, no warning */ ;

The Possible Errors option corresponds to the pragma warn_possunwant, described at "warn_possunwant." To check whether this option is on, use __option (warn_possunwant). See "Checking Options" for information on how to use this directive.