Methods and Parameters

Methods are the building blocks of C# programs. They encapsulate reusable logic, accept input through parameters, and return results. This lesson covers method declarations, parameter passing, overloading, and modern syntax.

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Defining Methods

A method has a return type, a name, and zero or more parameters:

// Method with return value
int Add(int a, int b)
{
    return a + b;
}

// Void method (no return value)
void PrintGreeting(string name)
{
    Console.WriteLine($"Hello, {name}!");
}

Calling Methods

int sum = Add(3, 5);       // 8
PrintGreeting("Alice");    // Hello, Alice!

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Expression-Bodied Methods

For simple one-line methods, use the => syntax:

int Add(int a, int b) => a + b;

string Greet(string name) => $"Hello, {name}!";

void Log(string message) => Console.WriteLine($"[LOG] {message}");

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Parameters

Default Parameters

void SendEmail(string to, string subject = "No Subject", int priority = 1)
{
    Console.WriteLine($"To: {to}, Subject: {subject}, Priority: {priority}");
}

SendEmail("alice@example.com");                          // Uses defaults
SendEmail("bob@example.com", "Meeting", 3);              // All specified
SendEmail("carol@example.com", priority: 5);             // Named argument

Named Arguments

Named arguments let you specify parameters in any order:

SendEmail(
    priority: 2,
    to: "dave@example.com",
    subject: "Urgent"
);

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Parameter Passing Modes

Keyword	Direction	Must Initialise Before Call	Must Assign in Method
(none)	In (by value)	Yes	No
ref	In/Out	Yes	No
out	Out	No	Yes
in	In (read-only ref)	Yes	No

Pass by Value (Default)

void Double(int x)
{
    x *= 2;  // Only modifies the local copy
}

int num = 5;
Double(num);
Console.WriteLine(num);  // Still 5

ref — Pass by Reference

void Double(ref int x)
{
    x *= 2;  // Modifies the original variable
}

int num = 5;
Double(ref num);
Console.WriteLine(num);  // 10

out — Output Parameter

bool TryDivide(int a, int b, out int result)
{
    if (b == 0)
    {
        result = 0;
        return false;
    }
    result = a / b;
    return true;
}

if (TryDivide(10, 3, out int quotient))
{
    Console.WriteLine($"Result: {quotient}");  // 3
}

in — Read-Only Reference

double CalculateDistance(in Point a, in Point b)
{
    // a and b are passed by reference but cannot be modified
    return Math.Sqrt(Math.Pow(b.X - a.X, 2) + Math.Pow(b.Y - a.Y, 2));
}

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