Halstead complexity measures

Halstead complexity measures are software metrics indroduced by Maurice Howard Halstead in 1977. These metrics are computed statically, without program execution.

Calculation

First we need to compute the following numbers, given the program:

• ${\displaystyle n1}$  = the number of distinct operators
• ${\displaystyle n2}$  = the number of distinct operands
• ${\displaystyle N1}$  = the total number of operators
• ${\displaystyle N2}$  = the total number of operands

From these numbers, five measures can be calculated:

• Program length:${\displaystyle N=N1+N2\,}$ 
• Program vocabulary: ${\displaystyle n=n1+n2\,}$ 
• Volume: ${\displaystyle V=N\times \log _{2}n\,}$ 
• Difficulty : ${\displaystyle D={n_{1} \over 2}\times {N_{2} \over n_{2}}\,}$ 
• Effort: ${\displaystyle E=D*V\,}$ 

The difficulty measure is related to the difficulty of the program to write or understand, e.g. when doing code review.

See also

• Function point
• Cyclomatic complexity