Cyclomatic complexity metric was firstly introduced by Thomas J. McCabe in 1976,  based on control flow representation of the program.

• It is used to refer the complexity of the program(source code).
• It is a measure of  the number of independent paths in a source code of the program that is correlated to n number of coding errors.
• The number of linearly- independent paths through a program is measured  using control flow graph to calculate the cyclomatic complexity.
• It is calculated as reference to classes, method's, modules and function within a program.

Cyclomatic Complexity V(G) = E- N+2

Where E= Total no. of edge in the flow graph
N= Number of nodes in the flow graph

Properties of Cyclomatic complexity:

• Maximum number of independent path are equal to V(G)
• Cyclomatic complexity can be equal to 1 or more than 1.
• If cycolmatic complexity equal to 1 then graph will have one path.
• Complexity Number 1-10 represents that code is written in good structured way and efforts and costs are low.
• If complexity number is 10-20  means  complex code and cost and effort is medium
• If complexity number is 20-40 means Very complex code and cost and effort is high
• If complexity number is >40 means cost and effort is very high

How useful is:

• In white box testing, basis path testing ensures to execute atleast one statement during testing
• To determine the total number of test cases required for complete coverage of the module.