Why is this an issue?

The switch statement is a conditional statement that executes a sequence of instructions based on patterns matching the provided value.

switch (temperatureInCelsius)
{
    case < 35.0:
        Console.WriteLine("Hypothermia");
        break;
    case >= 36.5 and <= 37.5:
        Console.WriteLine("Normal");
        break;
    case > 37.5 and <= 40.0:
        Console.WriteLine("Fever or hyperthermia");
        break;
    case > 40.0:
        Console.WriteLine("Hyperpyrexia");
        break;
}

The switch statement can optionally contain a default clause, executed when none of the case clauses are executed (or in presence of a goto default;).

switch (gradeLetter)
{
    case "A+":
    case "A":
    case "A-":
        Console.WriteLine("Excellent");
        break;
    case "B+":
    case "B":
        Console.WriteLine("Very Good");
        break;
    case "B-":
    case "C+":
        Console.WriteLine("Good");
        break;
    case "C":
        Console.WriteLine("Pass");
        break;
    case "F":
        Console.WriteLine("Fail");
        break;
    default:
        Console.WriteLine("Invalid grade letter!");
        break;
}

The default clause can be defined for various reasons:

• to handle unexpected values, as shown in the example above
• or to show that all the cases were properly considered, making the function explicitely total (as opposed to partial)

While C# allows the default clause to appear in any place within a switch statement, and while its position doesn’t alter its behavior, it is recommended to put the default clause either at the beginning or at the end of the switch statement.

That improves readability and helps the developer to quickly find the default behavior of a switch statement.

This rule raises an issue if the default clause is neither the first nor the last one of the switch statement.

How to fix it

Code examples

Noncompliant code example

switch (param)
{
    case 0:
        DoSomething();
        break;
    default: // Noncompliant: default clause should be the first or last one
        Error();
        break;
    case 1:
        DoSomethingElse();
        break;
}

Compliant solution

switch (param)
{
    case 0:
        DoSomething();
        break;
    case 1:
        DoSomethingElse();
        break;
    default:
        Error();
        break;
}

Resources

Documentation

• Switch statement
• Partial function