This document discusses code metrics and why they are important. It defines various code metrics like length, vocabulary, difficulty, volume, effort, bugs, structuredness, complexity, and maintainability. It discusses pioneers in code metrics like Thomas McCabe and Maurice Halstead. It provides examples of calculating Halstead metrics like length, vocabulary, difficulty, volume, effort, and bugs for sample code. It also discusses metrics like cyclomatic complexity, class coupling, depth of inheritance, and maintainability index. Finally, it mentions that metrics can be measured at the method, class, package and system levels.

1. CODE METRICS
Eng. Mohammad R. Katby

2. Which line of code easier to understand?
int x = x + 1;
int x = y + 1;
or
CODE METRICS Eng. Mohammad R. Katby

3. Agenda
■ What are the code measurement units?
■ What we are going to measure?
■ Why we need code metrics
■ What are code metrics

5. What are Code Metrics
■ Length
■ Vocabulary
■ Difficulty
■ Volume
■ Effort
■ Bugs
■ Structuredness
■ Complexity
■ Maintainability
■ Independability

6. Why we need measurements?
■ Without measurement you cannot understand code faults
■ See whether improvement can be made or not
■ Simply you can’t be Electrician if you can’t measure the voltage

7. Pioneers of Code Metrics
Thomas J. McCabe - 1976 Maurice Halstead - 1977

8. int x = x + 1;
Operators
Operands
Operand: 4, Unique: 3
Operator: 3, Unique: 3
OD = 4; UOD = 3
OP = 3; UOP = 3

9. Halstead metrics “Primitives”
■ Length (LTH) = OP + OD = 3 + 4 = 7
■ Vocabulary (VOC) = UOP + UOD = 3 + 3 = 6
■ Difficulty (DIF) = (UOP / 2) * (OD / UOD) = (3 / 2) * (4 / 3) = 1.99
■ OP = 3, UOP = 3, OD = 4, UOD = 4
■ LTH = 3 + 4 = 7
■ VOC = 3 + 4 = 7
■ DIF = (3 / 2) * (4 / 4) = 1.5
int x = x + 1;
int x = y + 1;

10. Halstead metrics “Derived”
■ Volume (VOL) = LTH * Log2(VOC) = 7 * 2.58 = 18.06
– You can view this as the ‘bulk’ of the code
– how much information does the reader of the code have to absorb to understand
its meaning
– biggest influence on theVolume metric is the Halstead length

11. Halstead metrics “Derived”
■ Bugs (BUG) =VOL / 3000 = 18.06 / 3000
– Estimates how many bugs you are likely to find in the system.

12. Halstead metrics “Derived”
■ Effort (EFF) = DIF *VOL = 1.99 * 18.06 = 38.96 / 18 = 2.16 (sec)
– The amount of mental effort required to recreate the software

13. Cyclomatic Complexity
■ Counting the number of decisions made in our source code.
■ Determine number test cases that need to be written
■ there is no exact limit that fits all organizations. However, a limit
of 10 is a good for such our industry
■ Measure: Strcuturedness, Complexity

14. Class Coupling
■ Measure how many classes a single class uses
■ Has been shown to be an accurate predictor of software failure
■ High coupling indicates design that is difficult to reuse and maintain
■ There is no limit that fits all organizations. However, a limit of 9 is optimal
■ Measure: Reusability, Maintainability,Changeability

15. Depth of Inheritance
■ The maximum length from the node to the root of the tree
■ Harder to predict behavior
■ Increase complexity of design since more classes and methods are involved
■ Have a greater potential for reusing
■ Several researches suggest that a DIT around 5 or 6 should be an upper limit

16. Maintainability Index
■ High value means better maintainability.
– LOW - red rating is a rating between 0 and 9
– MODERIATE - yellow rating is between 10 and 19
– GOOD - green rating is between 20 and 100
■ Maintainability Index = MAX(0,(171 – 5.2 * log(HalsteadVolume) – 0.23 * (Cyclomatic
Complexity) – 16.2 * log(Lines of Code))*100 / 171)
■

17. Levels of Measurement
■ Method
■ Class
■ Package and system

18. References
■ http://moosehead.cis.umassd.edu/cis580/readings/OO_Design_Complexity_Metrics.p
df
■ http://www.mccabe.com/pdf/mccabe-nist235r.pdf
■ http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.104.4041&rep=rep1&type=
pdf
■ http://www.campwoodsw.com/sourcemonitor.html
■ https://sourceforge.net/projects/metrics/