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Avoid excessive complexity

TypeName

AvoidExcessiveComplexity

CheckId

CA1502

Category

Microsoft.Maintainability

Breaking Change

Non Breaking

A method has an excessive cyclomatic complexity.

Cyclomatic complexity measures the number of linearly independent paths through the method, which is determined by the number and complexity of conditional branches. A low cyclomatic complexity generally indicates a method that is easy to understand, test, and maintain. The cyclomatic complexity is calculated from a control flow graph of the method and is given as follows:

cyclomatic complexity = the number of edges - the number of nodes + 1

where a node represents a logic branch point and an edge represents a line between nodes.

The rule reports a violation when the cyclomatic complexity is more than 25.

To fix a violation of this rule, refactor the method to reduce its cyclomatic complexity.

It is safe to suppress a warning from this rule if the complexity cannot easily be reduced and the method is easy to understand, test, and maintain. In particular, a method that contains a large switch (Select in Visual Basic) statement is a candidate for exclusion. The risk of destabilizing the code base late in the development cycle or introducing an unexpected change in runtime behavior in previously shipped code might outweigh the maintainability benefits of refactoring the code.

Basically, the cyclomatic complexity is calculated by adding 1 to the following:

  • Number of branches (such as if, while, and do)

  • Number of case statements within a switch

The following examples show methods with varying cyclomatic complexities.

Cyclomatic Complexity of 1

void Method()
{
	Console::WriteLine("Hello World!");
}

Cyclomatic Complexity of 2

void Method(bool condition)
{ 
  if (condition)
	{ 
		Console::WriteLine("Hello World!"); 
	} 
}

Cyclomatic Complexity of 3

void Method(bool condition1, bool condition2)
{
	if (condition1 || condition2)
	{
		Console::WriteLine("Hello World!");
	}
}

Cyclomatic Complexity of 8

void Method(DayOfWeek day)
{
	switch (day)
	{
		case DayOfWeek::Monday:
			Console::WriteLine("Today is Monday!");
			break;
		case DayOfWeek::Tuesday:
			Console::WriteLine("Today is Tuesday!");
		break;
		case DayOfWeek::Wednesday:
			Console::WriteLine("Today is Wednesday!");
		break;
		case DayOfWeek::Thursday:
			Console::WriteLine("Today is Thursday!");
		break;
		case DayOfWeek::Friday:
			Console::WriteLine("Today is Friday!");
		break;
		case DayOfWeek::Saturday:
			Console::WriteLine("Today is Saturday!");
		break;
		case DayOfWeek::Sunday:
			Console::WriteLine("Today is Sunday!");
		break;
	}
}
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