Optional and Named Arguments

Not every parameter needs a value on every call. C# lets you give parameters defaults, and lets callers name arguments explicitly for clarity.

Optional parameters

A parameter with a default value becomes optional:

static void Greet(string name, string greeting = "Hello")
{
    Console.WriteLine($"{greeting}, {name}!");
}

Greet("Ada");              // "Hello, Ada!"
Greet("Ada", "Welcome");   // "Welcome, Ada!"

Optional parameters must come after all required ones — you can't have a required parameter follow an optional one, since the compiler matches positionally by default:

// Invalid: required parameter can't follow an optional one
static void Greet(string greeting = "Hello", string name) { }

Named arguments

Named arguments let you specify which parameter you're supplying by name, independent of position:

static void CreateUser(string name, int age, bool isAdmin = false)
{
    Console.WriteLine($"{name}, {age}, admin={isAdmin}");
}

CreateUser(name: "Ada", age: 30, isAdmin: true);
CreateUser(age: 30, name: "Ada"); // order doesn't matter with named arguments

This is especially valuable with several bool or same-typed parameters in a row, where a plain positional call like CreateUser("Ada", 30, true) forces the reader to go check the method signature just to know what true means. Compare:

// Unclear at the call site
ScheduleMeeting("Standup", true, false);

// Clear, self-documenting
ScheduleMeeting("Standup", isRecurring: true, sendReminder: false);

Combining both

Named arguments also let you skip earlier optional parameters and only supply a later one:

static void Configure(int retries = 3, int timeoutMs = 1000, bool verbose = false)
{
    // ...
}

Configure(verbose: true); // retries and timeoutMs keep their defaults

Without named arguments, you'd have to repeat 3 and 1000 explicitly just to reach verbose. Together, optional and named arguments let a method support a wide range of call patterns without you having to write a pile of overloads to cover each combination.