DCL06-A Use meaningful symbolic constants to represent literal values

Avoid the use of numerical values or "magic numbers" in code when possible. Rather, use appropriately named symbolic constants clarify the intent of the code. In addition, if a specific value needs to be changed reassigning a symbolic constant once is more efficient and less error prone then replacing every instance of the value to be changed.

Non Compliant Code Example

The meaning of the numeric literal 18 is not clear in this example.

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 declare them as a constant in accordance with [[DCL00-A]].

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

Risk Assessment

Using numeric literals makes code more difficult to read and understand.

References

http://www.doc.ic.ac.uk/lab/cplus/c++.rules/chap10.html
[[ISO/IEC 9899-1999]] Section 6.7, "Declarations"