Avoid excessive complexity

TypeName	AvoidExcessiveComplexity
CheckId	CA1502
Category	Microsoft.Maintainability
Breaking Change	Non Breaking

Cause

A method has an excessive cyclomatic complexity.

Rule Description

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.

How to Fix Violations

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

When to Suppress Warnings

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.

How Cyclomatic Complexity is Calculated

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.

Example

Cyclomatic Complexity of 1

Public Sub Method()
    Console.WriteLine("Hello World!")
End Sub

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

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

Cyclomatic Complexity of 2

Public Sub Method(ByVal condition As Boolean)
    If (condition) Then
        Console.WriteLine("Hello World!")
    End If 
End Sub

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

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

Cyclomatic Complexity of 3

Public Sub Method(ByVal condition1 As Boolean, ByVal condition2 As Boolean)
    If (condition1 OrElse condition2) Then
        Console.WriteLine("Hello World!")
    End If 
End Sub

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

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

Cyclomatic Complexity of 8

Public Sub Method(ByVal day As DayOfWeek)
    Select Case day
        Case DayOfWeek.Monday
            Console.WriteLine("Today is Monday!")
        Case DayOfWeek.Tuesday
            Console.WriteLine("Today is Tuesday!")
        Case DayOfWeek.Wednesday
            Console.WriteLine("Today is Wednesday!")
        Case DayOfWeek.Thursday
            Console.WriteLine("Today is Thursday!")
        Case DayOfWeek.Friday
            Console.WriteLine("Today is Friday!")
        Case DayOfWeek.Saturday
            Console.WriteLine("Today is Saturday!")
        Case DayOfWeek.Sunday
            Console.WriteLine("Today is Sunday!")
    End Select 
End Sub

public 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;
        }
    }

}

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;
    }
}

Related Rules

Avoid excessive inheritance