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enum { ADULT_AGE=18 };
/* ... */
if (age >= ADULT_AGE) {
   /* Take action */
}
else {
  /* Take a different action */
}
/* ... */

Non-Compliant Code Example

Magic numbers are frequently used when referring to array dimensions, as shown in this non-compliant coding example.

char buffer[256];
/* ... */
fgets(buffer, 256, stdin);

This use of magic numbers can easily result in buffer overflows, if for example, the buffer size is reduced but the magic number used in the call to fgets() is not.

Compliant Solution (enum)

In this compliant solution the magic number is replaced with an enumeration constant (see DCL00-A. Declare immutable values using enum or const).

enum { BUFFER_SIZE=256 };

char buffer[BUFFER_SIZE];
/* ... */
fgets(buffer, BUFFER_SIZE, stdin);

Compliant Solution (((sizeof}})

A sizeof expression can work just as well as an enumeration constant (see EXP09-A. Use sizeof to determine the size of a type or variable).

char buffer[256];
/* ... */
fgets(buffer, sizeof(buffer), stdin);

Using the sizeof expression reduces the total number of names declared in the program, which is almost always a good thing to do.

Exceptions

DCL06-EX1: While replacing numeric constants with a symbolic constant is often a good practice, it can be taken too far. Exceptions can be made for constants that are themselves the abstraction you want to represent, as in this compliant solution.

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