Cyclomatic complexity is a software metric (measurement). 
It was developed by Thomas McCabe and is used to measure 
the complexity of a program. It directly measures the 
number of linearly independent paths through a program's 
source code. It is computed using a graph that describes 
the control flow of the program. The nodes of the graph 
correspond to the commands of a program. A directed edge 
connects two nodes if the second command might be executed 
immediately after the first command.


Definition

M = E − N + 2P

where

M = cyclomatic complexity
E = the number of edges of the graph
N = the number of nodes of the graph
P = the number of connected components.

"M" is alternatively defined to be one larger than the 
number of decision points (if/case-statements, while-
statements, etc) in a module (function, procedure, chart 
node, etc.), or more generally a system.

Separate subroutines are treated as being independent, 
disconnected components of the program's control flow graph.