What is Cyclomatic Complexity and how it is computed?

Cyclomatic complexity measures the amount of decision logic in a single software module. It provides a quantitative measure of the logical complexity of a program. It gives the number of recommended test for software. When used in the context of basis path testing method, the value computed for Cyclomatic complexity defines the number for independent paths in the basis set of a program and provides us an upper bound for the number of tests that must be conducted to ensure that all statements have been executed at least once.
An independent path is any path through the program that introduces at least one new set of processing statements or a new condition.

Control flow graphs describe the logic structure of software module. Each flow consists of nodes and edges. Nodes are computation statements or expresions.
Edges represent transfer of control between nodes.Each possible execution path of a software module has a corresponding path from the entry to the exit node of the module's control flow graph.

Computing Cyclomatic Complexity
Cyclomatic complexity has a foundation in graph theory and provides us with extremely useful software metric. Complexity is computed in one of the three ways:
- The number of regions of the flow graph corresponds to the cyclomatic complexity.
- Cyclomatic complexity, V(G), for a flow graph, G is defined as:
V(G)= E-N+2
where E is the number of flow graph edges and N is the number of flow graph nodes.
- Cyclomatic complexity, V(G) for a flow graph, G is also defined as:
V(G)= P+1
where P is the number of predicate nodes contained in the flow graph G.