Common causes of Cyclomatic Complexity and their solutions

Question

At work we are looking into common problems that lead to high cyclomatic complexity. For example, having a large if-else statement can lead to high cyclomatic complexity, but can be resolved by replacing conditionals with polymorphism. What other examples have you found?

Answer 1

See the NDepend's definition of Cyclomatic Complexity.

Nesting Depth is also a great code metric.

Cyclomatic complexity is a popular procedural software metric equal to the number of decisions that can be taken in a procedure. Concretely, in C# the CC of a method is 1 + {the number of following expressions found in the body of the method}:

if | while | for | foreach | case | default | continue | goto | && | || | catch | ternary operator ?: | ??

Following expressions are not counted for CC computation:

else | do | switch | try | using | throw | finally | return | object creation | method call | field access

Adapted to the OO world, this metric is defined both on methods and classes/structures (as the sum of its methods CC). Notice that the CC of an anonymous method is not counted when computing the CC of its outer method.

Recommendations: Methods where CC is higher than 15 are hard to understand and maintain. Methods where CC is higher than 30 are extremely complex and should be split in smaller methods (except if they are automatically generated by a tool).