C# — Methods

Basic methods

using System;

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

    // Expression-bodied method
    public int Multiply(int a, int b) => a * b;

    // Void method
    public void PrintSum(int a, int b)
    {
        Console.WriteLine($"{a} + {b} = {a + b}");
    }

    static void Main()
    {
        var calc = new Calculator();
        Console.WriteLine(calc.Add(3, 4));       // 7
        Console.WriteLine(calc.Multiply(3, 4));  // 12
        calc.PrintSum(3, 4);                     // 3 + 4 = 7
    }
}

Parameters

using System;

class Examples
{
    // Value parameters
    static void ByValue(int x)
    {
        x = 100; // Only changes local copy
    }

    // Reference parameters
    static void ByReference(ref int x)
    {
        x = 100; // Changes the original
    }

    // Out parameters
    static void Divide(int a, int b, out int quotient, out int remainder)
    {
        quotient = a / b;
        remainder = a % b;
    }

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

    // Named arguments
    static void CreateProfile(string name, int age, string city = "Unknown")
    {
        Console.WriteLine($"{name}, {age}, {city}");
    }

    static void Main()
    {
        int a = 5;
        ByValue(a);
        Console.WriteLine($"After ByValue: {a}"); // 5

        ByReference(ref a);
        Console.WriteLine($"After ByReference: {a}"); // 100

        Divide(10, 3, out int q, out int r);
        Console.WriteLine($"10 / 3 = {q} remainder {r}");

        Greet("Alice");            // Hello, Alice!
        Greet("Bob", "Hi");       // Hi, Bob!

        // Named arguments
        CreateProfile(age: 30, name: "Alice", city: "NYC");
    }
}

Params

using System;

class Stats
{
    static int Sum(params int[] numbers)
    {
        int total = 0;
        foreach (int n in numbers)
            total += n;
        return total;
    }

    static void Main()
    {
        Console.WriteLine(Sum(1, 2, 3));         // 6
        Console.WriteLine(Sum(1, 2, 3, 4, 5));   // 15
    }
}

Method overloading

using System;

class Printer
{
    static void Print(int value) => Console.WriteLine($"Int: {value}");
    static void Print(double value) => Console.WriteLine($"Double: {value}");
    static void Print(string value) => Console.WriteLine($"String: {value}");
    static void Print(int[] values) =>
        Console.WriteLine($"Array: [{string.Join(", ", values)}]");

    static void Main()
    {
        Print(42);          // Int: 42
        Print(3.14);        // Double: 3.14
        Print("hello");     // String: hello
        Print(new[] { 1, 2, 3 }); // Array: [1, 2, 3]
    }
}

Local functions

using System;

class Program
{
    static void Main()
    {
        // Local function inside Main
        int Factorial(int n)
        {
            if (n <= 1) return 1;
            return n * Factorial(n - 1);
        }

        Console.WriteLine($"5! = {Factorial(5)}");

        // Lambda-style local function
        int Square(int x) => x * x;
        Console.WriteLine($"5² = {Square(5)}");
    }
}

Static methods

using System;

class MathHelper
{
    // Static method — called on the class, not an instance
    public static double CircleArea(double radius)
    {
        return Math.PI * radius * radius;
    }

    public static int Max(int a, int b) => a > b ? a : b;
}

class Program
{
    static void Main()
    {
        Console.WriteLine(MathHelper.CircleArea(5));  // 78.5398
        Console.WriteLine(MathHelper.Max(3, 7));     // 7
    }
}

Async methods

using System;
using System.Threading.Tasks;

class DataFetcher
{
    static async Task<string> FetchDataAsync(string url)
    {
        // Simulate async work
        await Task.Delay(1000);
        return $"Data from {url}";
    }

    static async Task Main()
    {
        Console.WriteLine("Fetching...");
        string result = await FetchDataAsync("https://api.example.com");
        Console.WriteLine(result);
    }
}

Delegates

using System;

// Define delegate type
delegate int MathOperation(int a, int b);

class Program
{
    static int Add(int a, int b) => a + b;
    static int Multiply(int a, int b) => a * b;

    static void Main()
    {
        MathOperation op = Add;
        Console.WriteLine(op(3, 4)); // 7

        op = Multiply;
        Console.WriteLine(op(3, 4)); // 12

        // Using Func and Action
        Func<int, int, int> addFunc = (a, b) => a + b;
        Action<string> printAction = s => Console.WriteLine(s);

        Console.WriteLine(addFunc(5, 3));
        printAction("Hello!");
    }
}

Mini Practice

Write C# code that:

1. Creates methods with ref and out parameters
2. Demonstrates method overloading
3. Uses a local function for recursion
4. Creates an async method

Up Next

In the next lesson, you'll learn about Classes — object-oriented programming in C#.