Below is pseudo-code which calculates a customer's cruise credits based on past cruise history:PROGRAM CALC...

A data flow anomaly occurs when a variable is used in an illogical manner within a program. The anomalies are typically classified into the following categories:

Defined but not Used (d-u): A variable is assigned a value, but the value is never utilized.

Declared but not Defined (d): A variable is declared but not given an initial value.

Killed before being Defined (k-d): A variable is released or nullified before any value is assigned to it.

Defined twice before Use (d-d): A variable is assigned a value multiple times without being used between definitions.

In the given pseudocode, Cruise_Length is declared at the beginning but it is neither assigned any value (defined) nor used anywhere in the program. This makes it a case of "Defined but not Used".

References:

This explanation is derived from standard definitions and explanations of data flow anomalies in the context of software testing and static analysis, which are part of the ISTQB CTAL-TTA syllabus and testing principles.