C#

TL;DR

One-liner: C# is Java done right - with LINQ, async/await, and less ceremony.

Core Strengths:

• Versatile (web, desktop, games, mobile, cloud)
• Best-in-class async programming with async/await
• LINQ for elegant data manipulation
• Cross-platform via .NET Core

Philosophy

C# balances power and productivity:

• Strongly typed, but concise - Type inference, var, and pattern matching reduce boilerplate
• Multi-paradigm - OOP by default, functional features when needed
• Evolving rapidly - Major features every year (records, pattern matching, primary constructors)
• Enterprise-grade - Designed for large codebases with proper tooling

C# started as “Java with properties” and evolved into one of the most feature-rich languages.

Quick Start

Install

# macOS
brew install dotnet

# Linux (Ubuntu)
sudo apt install dotnet-sdk-10.0

# Windows - download from dotnet.microsoft.com

Verify (latest: .NET 10 / C# 14)

dotnet --version  # 10.0.100

First Program

dotnet new console -n Hello
cd Hello
dotnet run

Or create Program.cs:

Console.WriteLine("Hello, World!");

dotnet run

Language Essentials

Variables & Types

// Type inference
var name = "Alice";    // string
var age = 25;          // int
var price = 19.99m;    // decimal

// Explicit types
string? nullable = null;
int[] numbers = [1, 2, 3];

// Collections
var list = new List<int> { 1, 2, 3 };
var dict = new Dictionary<string, int> { ["a"] = 1 };

Control Flow

// if-else
if (age >= 18)
    Console.WriteLine("Adult");
else
    Console.WriteLine("Minor");

// Switch expression (C# 8+)
var status = age switch
{
    < 13 => "Child",
    < 20 => "Teen",
    _ => "Adult"
};

// Pattern matching
if (obj is string s && s.Length > 0)
{
    Console.WriteLine(s);
}

// foreach
foreach (var item in list)
{
    Console.WriteLine(item);
}

Functions (Methods)

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

// Default parameters
void Log(string msg, string level = "INFO")
{
    Console.WriteLine($"[{level}] {msg}");
}

// Named arguments
Log(level: "ERROR", msg: "Failed");

// Local functions
int Outer(int x)
{
    return Inner(x * 2);
    int Inner(int y) => y + 1;
}

Async/Await

// Async method
async Task<string> FetchDataAsync(string url)
{
    var client = new HttpClient();
    return await client.GetStringAsync(url);
}

// Usage
var data = await FetchDataAsync("https://api.example.com");

// Parallel async
var tasks = urls.Select(FetchDataAsync);
var results = await Task.WhenAll(tasks);

LINQ

var numbers = new[] { 1, 2, 3, 4, 5 };

// Query syntax
var evens = from n in numbers
            where n % 2 == 0
            select n;

// Method syntax (more common)
var doubled = numbers
    .Where(n => n > 2)
    .Select(n => n * 2)
    .ToList();

// Works on anything: arrays, lists, databases, XML...

Records & Classes

// Record (immutable data, C# 9+)
public record User(string Name, int Age);

var user = new User("Alice", 25);
var older = user with { Age = 26 };

// Class with primary constructor (C# 12+)
public class Service(ILogger logger)
{
    public void Log(string msg) => logger.Log(msg);
}

Gotchas

Nullable reference types

// Enabled by default in .NET 6+
string? nullable = null;     // OK
string nonNull = null;       // Warning CS8600

// Null-forgiving operator (when you know better)
string value = GetPossiblyNull()!;

Value types vs Reference types

int a = 5;
int b = a;  // b is a copy

int[] arr1 = [1, 2, 3];
int[] arr2 = arr1;  // Same reference!
arr2[0] = 99;       // arr1[0] is also 99

async void is dangerous

// Bad - can't await, exceptions are lost
async void BadMethod() { }

// Good - use Task
async Task GoodMethod() { }

// Only exception: event handlers
button.Click += async (s, e) => { };

LINQ is lazy

var query = list.Where(x => x > 5);  // Nothing happens yet

// Forces execution
var result = query.ToList();
var first = query.First();
foreach (var x in query) { }

When to Choose

Best for:

• Enterprise applications (.NET ecosystem)
• Game development (Unity)
• Windows applications (WPF, WinForms)
• Cross-platform mobile (MAUI, Xamarin)

Not ideal for:

• System programming (use Rust, C++)
• Quick scripts (use Python)
• Linux-only shops unfamiliar with .NET

Comparison:

Aspect	C#	Java	TypeScript
Async	Excellent	Good	Excellent
Ecosystem	Large	Huge	Large
Learning	Medium	Medium	Easy
Platform	.NET	JVM	Node/Browser

Next Steps

• C# Documentation
• .NET Tutorials
• C# Interactive
• ASP.NET Core - Web framework

Ecosystem

Project Types

dotnet new console    # Console app
dotnet new webapi     # REST API
dotnet new blazor     # Web UI
dotnet new maui       # Cross-platform mobile/desktop

Popular Libraries

• Web: ASP.NET Core, Blazor
• ORM: Entity Framework Core, Dapper
• Testing: xUnit, NUnit, Moq
• Logging: Serilog, NLog