Cyclomatic Complexity is the software metric used to indicate the complexity of a program as originally described by McCabe (see the Wikipedia entry for a reference).
Since the original definition of Cyclomatic Complexity is quite abstract (in terms of graphs), the definition used by TIOBE is loosely
The decision count plus one
The decision count is incremented for control flow statements that
introduce a branch in the code, e.g., selection statements
if-statement), iteration statements
while-statement) and exception handling
The Cyclomatic Complexity of a function (or method) is the number of decisions in the function's body plus one. So, the minimum cyclomatic complexity of a function definition is one.
The Cyclomatic Complexity of a file is the number of decisions of all function definitions in that file plus one. In other words, this is the sum of the cyclomatic complexities of all function definitions in the file, minus the number of function definitions, plus one.
The Average Cyclomatic Complexity is the cyclomatic complexity per function of a file. So, this is the sum of the cyclomatic complexities of all function definitions, divided by the number of function definitions in the file.
The Average Cyclomatic Complexity is aggregated over multiple files as follows. Sum the cyclomatic complexities of all files, minus the number of files, divided by the total number of function definitions in these files combined, plus one.
The TQI Cyclomatic Complexity submetric is described in The TIOBE Quality Indicator document, Section 5.
score = 800 / (cyclomatic_complexity^2 - 3*cyclomatic_complexity + 10)
There are a (great) number of free and commercial tools available that can be used to measure the (average) cyclomatic complexity of source files. Here, we will take a look at a few available options.
SourceMonitor is a freeware program to obtain cyclomatic complexity for many programming languages. It runs on Windows. The results reported by SourceMonitor are quite reasonable, especially when compared to e.g. CCCC (see below). A disadvantage is that it does not support all programming languages for which TIOBE wishes to compute cyclomatic complexity. Another drawback is that it can only be used on Windows, and not on e.g. Linux.
CCCC is an open source code counter for C, C++ and Java source files. It is reasonably cross-platform and can run on Windows and Linux. Unfortunately, its results are very unreliable. Moreover, it supports just a few programming languages.
There are many more tools available to measure cyclomatic complexity. Some commercial, or part of a commercial package, some specific to a certain programming language. We will not discuss these here.
At TIOBE, we compared the results of CCCC, SourceMonitor and TICSpp on a great number of (customer) source files and found that TICSpp produces better results than SourceMonitor, which in turn produces better results than CCCC. These findings, together with its portability and support for a wide range of programming languages makes TICSpp a logical default choice for our customers.
Be sure to use a default configuration, or specify
'METRICS'=>['TICSpp'], for your language in SERVER.txt.
The metric to run with TICS for Average Cyclomatic Complexity is
To run the TICS client, use
TICS -calc AVGCYCLOMATICCOMPLEXITY.
To run TICSQServer, use
TICSQServer -calc AVGCYCLOMATICCOMPLEXITY.
To quickly see "bad" files (wrt cyclomatic complexity) in TICS viewer, one can use the treemap and select the Average Cyclomatic Complexity as the color and Total Cyclomatic Complexity for the area metric.
The big, dark red files are the ones to go after first.