Page History

...

In this example, the programmer has mistakenly omitted the comparison operator (see MSC02-A. Avoid errors of omission) from the conditional statement, which should be getchar() != EOF. After macro expansion, the conditional expression is incorrectly evaluated as a binary operation: getchar()-1. This is syntactically correct, even though it is certainly not what the programmer intended. Note that this example also violates DCL00-A. Declare immutable values using enum or constobjects as constants.

Parenthesizing the -1 in the declaration of EOF ensures that the macro expansion is evaluated correctly.

...

In this compliant solution, we replace the macro definition with an enumeration constant in compliance with DCL00-A. Declare immutable values using enum or constobjects as constants.

enum { EOF = -1 };
/* ... */
if (getchar() != EOF) {
   /* ... */
}

...