Code Metrics - Maintainability Index

• This is an index from 0 to 100 indicating the overall maintainability of the member or type or program
• This index is based on the following metrics,
•  Halstead Volume (which factors in the number and use of operands and operators),
• Cyclomatic Complexity
• Lines of Code

Maintainability Index = 171 - 5.2 * log2 (Halstead Volume) - 0.23 * (Cyclomatic Complexity) - 16.2 * log2 (Lines of Code)

• A low number indicates code that is complex and hard to maintain
  

 VSTS2008 has the inbuilt maintainability measuring technique.


Maintainability Definition:

Range	Level
20-100 inclusive	High Maintainability
10-19 inclusive	Moderate Maintainability
0-9 inclusive	Low Maintainability

 

Product Metrics - Cyclomatic Complexity

Developed by Thomas J. McCabe Sr. in 1976. It is used to measure the complexity of a program. It directly measures the number of linearly independent paths through a program's source code. It is computed using the control flow graph of the program.

The simplest formula for calculating the Cyclomatic  Complexity is as follows

M = E – N + 2

 M = Cyclomatic Complexity
E = Number of edges in the control graph
N = Number of nodes in the control graph

 

Sample 1:

Simple If statement, the CC will be
M = 3 - 3 + 2 ==> 2 

Sample 2:
If-else statement, the CC will be
M = 4 - 4 +2 ==> 2

Sample 3:
Switch block, the CC will be
M = 6 - 5 + 2 ==> 3

VSTS 2008 has inbuilt product metrics measurement option for LOC, CC, coupling and maintainability index. SourceMonitor is another open source tool which helps to measure some of the the product metrics including CC.

Complexity definition:

Cyclomatic Complexity	Risk Evaluation
1 to 10	a simple program, without very much risk
11 to 20	a more complex program, moderate risk
21 to 50	a complex, high risk program
> 50	an un-testable program (very high risk)