Editing Cyclomatic complexity (section)

===Measuring the "structuredness" of a program===
{{Main|Essential complexity (numerical measure of "structuredness")}} <!-- please update the link when that article is split, as it should be -->
Section VI of McCabe's 1976 paper is concerned with determining what the control-flow graphs (CFGs) of non-[[structured programming|structured program]]s look like in terms of their subgraphs, which McCabe identified. (For details, see [[structured program theorem]].) McCabe concluded that section by proposing a numerical measure of how close to the structured programming ideal a given program is, i.e. its "structuredness". McCabe called the measure he devised for this purpose [[Essential complexity (numerical measure of "structuredness")|essential complexity]].<ref name="mccabe76" />

To calculate this measure, the original CFG is iteratively reduced by identifying subgraphs that have a single-entry and a single-exit point, which are then replaced by a single node. This reduction corresponds to what a human would do if they extracted a subroutine from the larger piece of code. (Nowadays such a process would fall under the umbrella term of [[refactoring]].) McCabe's reduction method was later called ''condensation'' in some textbooks, because it was seen as a generalization of the [[condensation (graph theory)|condensation to components used in graph theory]].<ref>{{cite book|author=Paul C. Jorgensen|title=Software Testing: A Craftsman's Approach, Second Edition|url=https://books.google.com/books?id=Yph_AwAAQBAJ&pg=PA150|year=2002|publisher=CRC Press|isbn=978-0-8493-0809-3|pages=150–153|edition=2nd}}</ref> If a program is structured, then McCabe's reduction/condensation process reduces it to a single CFG node. In contrast, if the program is not structured, the iterative process will identify the irreducible part. The essential complexity measure defined by McCabe is simply the cyclomatic complexity of this irreducible graph, so it will be precisely 1 for all structured programs, but greater than one for non-structured programs.<ref name="nist"/>{{rp|80}}<!--note that the original paper has an error here in that it subtracts the number of nodes from that [and thus can give negative essential complexity measures for some non-structured programs], but the later technical report fixed that]-->