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Non Compliant Code Example

The meaning of the value 18 is not clear in this example. Additionally, should this value need to be changed, the programmer would have to change it in multiple places.

if (age >= 18) {
   /* Take action */
}
...
if (age < 18) {
  /* Take a different action */
}

Compliant Solution

The compliant solution replaces 18 with the symbolic constant ADULT_AGE to clarify the meaning of the code.

When declaring immutable symbolic values such as ADULT_AGE it is best to use const or enum as explained in DCL00-A. Declare immutable values using const or enum.

enumint {const ADULT_AGE = 18 };
...
if (age >= ADULT_AGE) {
   /* Take action */
}
...
if (age < ADULT_AGE) {
  /* Take a different action */
}

In the compliant code it is easy to check if the user is an adult and process accordingly. If the definition of adult changes during iterations of the codebase it is much simpler to replace the value for ADULT_AGE in one place then search for instance of 18 and see if they're appropriate for change.

When declaring immutable symbolic values such as ADULT_AGE it is best to use const or enum as explained in

DCL00-A. Declare immutable values using const or enum 

Risk Assessment

Mistakes regarding numeric values can cause unintended consequences if changes are not made uniformly

Risk Assessment

Using numeric literals in code makes that code more difficult to read and understand the programmers intent.

References

Source: http://www.doc.ic.ac.uk/lab/cplus/c++.rules/chap10.html