🚀 C# Learning Journey

Day-by-Day Revision & Notes

A structured, beginner-to-proficient C# tutorial series with definitions, syntax, examples, and best practices.

Author: Arvind Kumar | GitHub: @arvind01A | Started: March 2026

🎉 Journey Completed!

10 days. Beginner → Expert. This repository is the complete C# Interview Roadmap — from fundamentals all the way to SOLID principles and Design Patterns. Thank you for following along! ⭐ Star this repo if it helped you.

📖 Overview

This repository documents my complete C# revision — from basics to expert-level concepts. Each day includes:

📌 What's Inside	Description
📝 Definitions	Clear, concise explanations
💻 Syntax Examples	Ready-to-reference patterns
📋 Code Snippets	Copy-paste ready code
⚠️ Pitfalls	Key differences & common mistakes
📊 Summary Tables	Quick-reference comparisons

💡 Perfect for beginners, self-learners, or anyone refreshing C# skills in 2026!

🎯 Roadmap — Completed ✅

Fundamentals → OOP → Collections → Exception Handling → File I/O → Expert_level-1 → Expert_level-2 → Expert_level-3
     ✅             ✅✅✅          ✅                    ✅           ✅               ✅                ✅

📅 All 10 Days — Complete

#	Day	Topic	Subtopics	Status
1	Day 1	Fundamentals	Variables · Operators · Control Flow · Loops	✅ Done
2	Day 2	Classes & Objects	Methods · Parameters · Constructors · Fields	✅ Done
3	Day 3	OOP Pillars	Encapsulation · Inheritance · Abstraction · Polymorphism	✅ Done
4	Day 4	Data Structures	Arrays · Strings · StringBuilder · Tuples	✅ Done
5	Day 5	Generics	Generic Classes · Methods · Constraints	✅ Done
6	Day 6	Collections	Non-Generic · Generic · Specialized · Concurrent	✅ Done
7	Day 7	Exception & File Handling	try-catch-finally · throw vs throw ex · Built-in Exceptions · StreamReader/Writer · Async File I/O	✅ Done
8	Day 8	Expert I — Functional Programming & Delegates	Extension Methods · Lambda · LINQ · Pattern Matching · Action/Func/Predicate · Events	✅ Done
9	Day 9	Expert II — Multithreading, Async & Serialization	Thread · Task · Parallel.ForEach · Async/Await · IAsyncEnumerable · JSON/XML/Binary	✅ Done
10	Day 10	Expert III — Best Practices & Design Patterns	Naming · Clean Code · Null Safety · C# 12 Features · SOLID · Creational · Structural · Behavioral Patterns	✅ Done

🏁 Completed: March 14, 2026

📚 Day-by-Day Notes

🟣 Day 1 — Fundamentals

Click to expand

📦 Variables & Data Types

int age = 25;
double price = 9.99;
string name = "Arvind";
bool isActive = true;
char grade = 'A';
var inferred = 42;          // Type inferred by compiler
const double PI = 3.14159;  // Constant

➕ Operators

// Arithmetic
int sum = 10 + 5;    // 15
int mod = 10 % 3;    // 1

// Comparison
bool isEqual = (5 == 5);   // true
bool notEqual = (5 != 4);  // true

// Logical
bool result = (true && false);  // false
bool either = (true || false);  // true

🔀 Control Statements

if (age >= 18) { Console.WriteLine("Adult"); }
else if (age >= 13) { Console.WriteLine("Teen"); }
else { Console.WriteLine("Child"); }

string label = age switch {
    >= 18 => "Adult",
    >= 13 => "Teen",
    _     => "Child"
};

🔁 Loops & Jump Statements

for (int i = 0; i < 5; i++) { }
while (condition) { }
do { } while (condition);
foreach (var item in collection) { }

break; continue; return; // jump statements

🔵 Day 2 — Classes & Objects

Click to expand

🏗️ Methods & Parameters

public int Add(int a, int b) => a + b;
public void Swap(ref int a, ref int b) { (a, b) = (b, a); }
public void TryParse(string s, out int result) { result = int.Parse(s); }
public void Greet(string name, string greeting = "Hello") =>
    Console.WriteLine($"{greeting}, {name}!");
Greet(name: "Arvind", greeting: "Hi");

🏛️ Constructors

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }

    public Person() { }
    public Person(string name) => Name = name;
    public Person(Person other) => (Name, Age) = (other.Name, other.Age);
    static Person() { /* runs once */ }
}

🗂️ Fields

public class Circle
{
    private double _radius;
    public static int Count = 0;
    public readonly double Id;
}

🟢 Day 3 — OOP Pillars

Click to expand

🔒 Encapsulation · 🧬 Inheritance · 🎭 Abstraction · 🔄 Polymorphism

// Encapsulation
public class BankAccount
{
    private decimal _balance;
    public decimal Balance { get => _balance; private set => _balance = value >= 0 ? value : 0; }
}

// Inheritance
public class Animal { public virtual void Speak() => Console.WriteLine("..."); }
public class Dog : Animal { public override void Speak() => Console.WriteLine("Woof!"); }

// Abstraction
public abstract class Shape { public abstract double Area(); }
public interface IDrawable { void Draw(); string Color { get; set; } }

// Polymorphism — runtime
Animal animal = new Dog();
animal.Speak();  // "Woof!"

Access Modifiers:

Modifier	Accessible From
`public`	Anywhere
`private`	Same class only
`protected`	Same class + subclasses
`internal`	Same assembly
`protected internal`	Same assembly or subclasses

🟡 Day 4 — Basic Data Structures

Click to expand

// Arrays
int[] nums = { 1, 2, 3, 4, 5 };
int[,] matrix = new int[3, 3];
int[][] jagged = new int[3][];
Array.Sort(nums); Array.Reverse(nums);

// Strings
string msg = $"Name: {name}, Age: {age}";
var sb = new StringBuilder();
sb.Append("Hello"); sb.AppendLine(" World");

// Tuples
var person = (Name: "Arvind", Age: 25, City: "Delhi");
var (name, age, city) = person;

🟠 Day 5 — Generics

Click to expand

public class Box<T> { public T Value { get; set; } }
public class Pair<TKey, TValue> { public TKey Key; public TValue Value; }
public static void Swap<T>(ref T a, ref T b) => (a, b) = (b, a);

Constraint	Meaning
`where T : class`	Reference types only
`where T : struct`	Value types only
`where T : new()`	Parameterless constructor
`where T : IComparable<T>`	Must implement IComparable

🔷 Day 6 — Collections

Click to expand

// Generic (preferred)
List<int> numbers       = new() { 1, 2, 3 };
var scores              = new Dictionary<string, int>();
var set                 = new HashSet<string>();
var sorted              = new SortedList<string, int>();

// Concurrent (thread-safe)
ConcurrentDictionary<string, int> dict = new();
ConcurrentQueue<string> queue           = new();

Collection	Ordered	Unique	Key-Value	Thread-Safe
`List<T>`	✅	❌	❌	❌
`Dictionary<K,V>`	❌	✅ Keys	✅	❌
`HashSet<T>`	❌	✅	❌	❌
`ConcurrentDictionary`	❌	✅ Keys	✅	✅

🔴 Day 7 — Exception & File Handling

Click to expand

// try-catch-finally
try   { int r = 10 / int.Parse("0"); }
catch (DivideByZeroException ex) { Console.WriteLine(ex.Message); }
finally { Console.WriteLine("Cleanup!"); }

// throw vs throw ex
catch (Exception ex) { Log(ex); throw; }        // ✅ preserves stack trace
catch (Exception ex) { Log(ex); throw ex; }      // ❌ resets stack trace

// File I/O
using var writer = new StreamWriter("notes.txt");
writer.WriteLine("Hello!");
string content = File.ReadAllText("notes.txt");
await File.WriteAllTextAsync("out.txt", "async write");
string path = Path.Combine("logs", "app.log");

🟤 Day 8 — Expert I: Functional Programming & Delegates

Click to expand

// Extension Methods
public static string Capitalize(this string s)
    => string.IsNullOrEmpty(s) ? s : char.ToUpper(s[0]) + s[1..];
"hello".Capitalize();  // "Hello"

// Lambda & LINQ
Func<int, int> square = x => x * x;
var result = students
    .Where(s => s.Score >= 80)
    .OrderByDescending(s => s.Score)
    .Select(s => s.Name);

// Pattern Matching
string desc = shape switch
{
    Circle c when c.Radius > 10 => "Large circle",
    Rectangle r                 => $"{r.Width}x{r.Height}",
    _                           => "Unknown"
};

// Delegates & Events
Action<string> greet = name => Console.WriteLine($"Hi {name}!");
Func<int, int> sq    = x => x * x;
Predicate<int> even  = n => n % 2 == 0;

public event EventHandler<OrderEventArgs> OrderPlaced;
OrderPlaced?.Invoke(this, new OrderEventArgs(item));

⚡ Day 9 — Expert II: Multithreading, Async & Serialization

Click to expand

// Thread
Thread t = new Thread(() => { Thread.Sleep(500); Console.WriteLine("Done"); });
t.IsBackground = true;  t.Start();  t.Join();

// Task (preferred)
Task<int> task = Task.Run(() => 42);
int result = await task;
int[] all = await Task.WhenAll(t1, t2, t3);

// Parallel (CPU-bound)
Parallel.ForEach(items, item => ProcessItem(item));
Parallel.Invoke(() => TaskA(), () => TaskB());

// Async/Await
public async Task<string> FetchAsync(string url)
{
    using var client = new HttpClient();
    return await client.GetStringAsync(url);
}

// Async Streams
await foreach (int num in GenerateNumbersAsync(10))
    Console.WriteLine(num);

// Serialization
string json = JsonSerializer.Serialize(person, new JsonSerializerOptions { WriteIndented = true });
Person? p   = JsonSerializer.Deserialize<Person>(json);

Format	Readable	Speed	Use Case
JSON	✅	Fast	APIs, web
XML	✅	Slow	Legacy, SOAP
Binary	❌	⚡ Fastest	Cache, IPC

🏆 Day 10 — Expert III: Best Practices & Design Patterns

Click to expand

✅ C# Best Practices

📛 Naming Conventions

// Classes, Methods, Properties → PascalCase
public class OrderService { }
public void PlaceOrder() { }
public string CustomerName { get; set; }

// Local variables, parameters → camelCase
int orderCount = 0;
void Process(string orderItem) { }

// Private fields → _camelCase
private readonly string _connectionString;

// Constants → PascalCase
public const int MaxRetries = 3;

// Interfaces → I prefix
public interface IOrderRepository { }

// Generics → T prefix
public class Repository<TEntity> { }

🧹 Clean Code Principles

// ✅ Small, focused methods
public async Task ProcessOrderAsync(Order order)
{
    await _validator.ValidateAsync(order);
    await _pricer.CalculateTotalAsync(order);
    await _repository.SaveAsync(order);
    await _notifier.SendConfirmationAsync(order);
}

// ✅ No magic numbers — use enums
public enum UserRole { Guest = 0, User = 1, Admin = 2 }
if (user.Role == UserRole.Admin) { }

// ✅ Expression bodies for simple members
public string FullName => $"{FirstName} {LastName}";

// ✅ Dispose resources
using var conn = new SqlConnection(connStr);
await using var stream = File.OpenWrite("out.txt");

🛡️ Null Safety (C# 8+)

string  name  = "Arvind";    // non-nullable
string? email = null;         // nullable

int? length = email?.Length;              // null-conditional
string display = name ?? "Anonymous";     // null-coalescing
cache ??= new Dictionary<string, int>();  // null-coalescing assignment

ArgumentNullException.ThrowIfNull(name);  // C# 10+ guard

// Required properties (C# 11+)
public class Order
{
    public required string Id { get; init; }
    public required string CustomerName { get; init; }
}

🆕 Modern C# Features (C# 10–14)

// Records (C# 9+)
public record Person(string Name, int Age);
var p2 = p1 with { Age = 26 };   // non-destructive mutation

// Global usings (C# 10+)
global using System.Text.Json;

// File-scoped namespace (C# 10+)
namespace MyApp.Services;

// Primary constructors (C# 12+)
public class OrderService(IOrderRepository repo, ILogger<OrderService> logger) { }

// Collection expressions (C# 12+)
int[] nums   = [1, 2, 3, 4, 5];
int[] merged = [..nums, 6, 7];

// Raw string literals (C# 11+)
string json = """
    {
        "name": "Arvind",
        "age": 25
    }
    """;

🏗️ SOLID Principles

S — Single Responsibility

// ❌ One class doing everything
// ✅ Separate concerns
public class UserRepository    { public void Save(User u) { } }
public class EmailService      { public void SendWelcome(User u) { } }
public class UserReportService { public string Generate(User u) => ""; }

O — Open/Closed

// ✅ Extend by adding new classes, never modify existing
public abstract class Shape       { public abstract double Area(); }
public class Circle    : Shape    { public override double Area() => Math.PI * Radius * Radius; }
public class Rectangle : Shape    { public override double Area() => Width * Height; }
public class Triangle  : Shape    { public override double Area() => 0.5 * Base * Height; }

L — Liskov Substitution

// ✅ Subclasses must honour base class contracts
public abstract class Shape    { public abstract double Area(); }
public class Rectangle : Shape { public int Width, Height; public override double Area() => Width * Height; }
public class Square    : Shape { public int Side;           public override double Area() => Side * Side; }

I — Interface Segregation

// ✅ Small focused interfaces
public interface IWorkable  { void Work(); }
public interface IEatable   { void Eat(); }
public class HumanWorker : IWorkable, IEatable { public void Work(){} public void Eat(){} }
public class RobotWorker : IWorkable           { public void Work(){} }

D — Dependency Inversion

// ✅ Depend on abstractions, inject implementations
public interface IOrderRepository { Task SaveAsync(Order o); }

public class OrderService
{
    private readonly IOrderRepository _repo;
    public OrderService(IOrderRepository repo) => _repo = repo;
    public async Task PlaceOrderAsync(Order o) => await _repo.SaveAsync(o);
}

// ASP.NET Core DI
builder.Services.AddScoped<IOrderRepository, SqlOrderRepository>();

🎨 Design Patterns

🏭 Singleton — one instance globally

public sealed class AppConfig
{
    private static readonly Lazy<AppConfig> _instance = new(() => new AppConfig());
    private AppConfig() { }
    public static AppConfig Instance => _instance.Value;
    public string ConnectionString { get; set; } = "";
}
AppConfig.Instance.ConnectionString = "Server=...";

🏭 Factory Method — decouple creation

public static Notification Create(string type) => type switch
{
    "email" => new EmailNotification(),
    "sms"   => new SmsNotification(),
    "push"  => new PushNotification(),
    _       => throw new ArgumentException($"Unknown: {type}")
};
Notification.Create("email").Send("Order confirmed!");

🏭 Builder — step-by-step construction

string query = new QueryBuilder()
    .From("Orders")
    .Where("Status = 'Active'")
    .Where("CustomerId = 42")
    .OrderBy("CreatedAt DESC")
    .Limit(10)
    .Build();

🔧 Repository — abstract data access

public interface IRepository<T> where T : class
{
    Task<T?> GetByIdAsync(int id);
    Task<IEnumerable<T>> GetAllAsync();
    Task AddAsync(T entity);
    Task DeleteAsync(int id);
}

🔧 Decorator — add behaviour without inheritance

// Base → CachedOrderService → LoggedOrderService
// Each wraps the inner and adds cross-cutting concerns
public class CachedOrderService : IOrderService
{
    private readonly IOrderService _inner;
    private readonly IMemoryCache  _cache;
    public async Task<Order> GetOrderAsync(int id)
    {
        if (_cache.TryGetValue(id, out Order? cached)) return cached!;
        var order = await _inner.GetOrderAsync(id);
        _cache.Set(id, order, TimeSpan.FromMinutes(5));
        return order;
    }
}

🔁 Observer — notify subscribers

public class StockTicker
{
    public event EventHandler<StockEventArgs>? PriceChanged;
    private decimal _price;
    public decimal Price { get => _price; set { _price = value; PriceChanged?.Invoke(this, new("AAPL", value)); } }
}
ticker.PriceChanged += (s, e) => Console.WriteLine($"[Alert] {e.Symbol}: ${e.Price}");

🔁 Strategy — swap algorithms at runtime

public interface ISortStrategy<T> { IEnumerable<T> Sort(IEnumerable<T> data); }
public class AscendingSort<T>  : ISortStrategy<T> where T : IComparable<T>
    { public IEnumerable<T> Sort(IEnumerable<T> d) => d.OrderBy(x => x); }
public class DescendingSort<T> : ISortStrategy<T> where T : IComparable<T>
    { public IEnumerable<T> Sort(IEnumerable<T> d) => d.OrderByDescending(x => x); }

var processor = new DataProcessor<int>(new AscendingSort<int>());
processor.SetStrategy(new DescendingSort<int>());  // swap at runtime

🔁 Chain of Responsibility — pipeline processing

var pipeline = new ValidationHandler();
pipeline.SetNext(new PricingHandler()).SetNext(new PersistenceHandler());
await pipeline.HandleAsync(order);
// ✅ Validated → ✅ Priced → ✅ Saved to DB

Design Patterns Quick Reference:

Category	Pattern	Problem Solved
Creational	Singleton	One instance needed globally
Creational	Factory Method	Decouple object creation
Creational	Builder	Complex multi-step construction
Structural	Repository	Abstract data access
Structural	Decorator	Add behaviour without inheritance
Behavioral	Observer	Notify multiple subscribers
Behavioral	Strategy	Swap algorithms at runtime
Behavioral	Chain of Responsibility	Pipeline / middleware processing

🗂️ Repository Structure

csharp-learning/
│
├── 📁 day1/                         ← Fundamentals
│   ├── 01-Variables/
│   ├── 02-Operators/
│   ├── 03-control-statements/
│   ├── 04-jump-statements/
│   └── 05-loops/
│
├── 📁 day2/                         ← Classes & Objects
│   ├── 01-Methods-and-Parameters/
│   │   ├── 01-Return-Types/
│   │   ├── 02-Parameter-Passing/
│   │   ├── 03-Optional-Parameters/
│   │   └── 04-Named-Arguments/
│   ├── 02-Constructors/
│   │   ├── 01-Default/
│   │   ├── 02-Parameterized/
│   │   ├── 03-Overloading/
│   │   └── 04-Static-and-Copy/
│   └── 03-Fields/
│
├── 📁 day3/                         ← OOP 4 Pillars
│   ├── 01-Encapsulation/
│   │   ├── 01-Access-Modifiers/
│   │   └── 02-Properties/
│   ├── 02-Inheritance/
│   │   ├── 01-Types-of-Inheritance/
│   │   └── 02-base-and-this-keywords/
│   ├── 03-Abstraction/
│   │   └── Abstract-Classes-and-Interfaces/
│   ├── 04-Polymorphism/
│   │   ├── 01-Compile-Time/
│   │   └── 02-Runtime/
│   └── 05-Indexers/
│
├── 📁 day4/                         ← Basic Data Structures
│   ├── Arrays/
│   │   ├── Single-Dimensional/
│   │   ├── Array-Methods/
│   │   ├── Array-Class/
│   │   └── Multi-Dim-and-Jagged/
│   ├── Strings/
│   │   ├── String-Operations/
│   │   ├── Interpolation/
│   │   └── String-vs-StringBuilder/
│   └── Tuples/
│       └── Named-Tuples/
│
├── 📁 day5/                         ← Generics
│   ├── Generic-Classes/
│   │        ├── Box<T>
│   │        ├── Pair<TKey
│   │        └── TValue>
│   ├── Generic-Methods/
│   │        ├── Explicit
│   │        └── Type Inference
│   └── Constraints/
│            ├── class
│            ├── struct
│            ├── new()
│            └── IComparable
│
├── 📁 day6/                         ← Collections/ Advance Data Structures
│   ├── Non-Generic/                 
│   │        ├── ArrayList
│   │        ├── Hashtable
│   │        ├── Queue
│   │        └── Stack
│   ├── Generic/                     
│   │        ├── List<T>
│   │        ├── Dictionary
│   │        ├── HashSet
│   │        └── LinkedList
│   └── Specialized/                 
│            └── Concurrent Collections
│
├── 📁 day7/                         ← Exception & File Handling
│   ├── Exception-Handling/
│   └── File-Handling/
│
├── 📁 day8/                         ← Expert I: Functional Programming & Delegates
│   ├── Functional-Programming/
│   ├── Delegates/
│   └── Events/
│
├── 📁 day9/                         ← Expert II: Multithreading, Async & Serialization
│   ├── Multithreading/
│   │   ├── 01-Thread-Class/
│   │   ├── 02-Task-Class/
│   │   └── 03-Parallel-ForEach/
│   ├── Async-Programming/
│   │   ├── 01-Async-and-Await/
│   │   ├── 02-Exception-Handling-in-Async/
│   │   └── 03-Async-Streams-IAsyncEnumerable/
│   └── Serialization/
│       ├── 01-JSON-Serialization/
│       ├── 02-XML-Serialization/
│       └── 03-Binary-Serialization/
│
├── 📁 day10/                        ← Expert III: Best Practices & Design Patterns
│   ├── Best-Practices/
│   │   ├── 01-Naming-Conventions/
│   │   ├── 02-Clean-Code/
│   │   ├── 03-Null-Safety/
│   │   └── 04-Modern-CSharp-Features/
│   └── SOLID-and-Design-Patterns/
│       ├── 01-SOLID-Principles/
│       │   ├── S-Single-Responsibility/
│       │   ├── O-Open-Closed/
│       │   ├── L-Liskov-Substitution/
│       │   ├── I-Interface-Segregation/
│       │   └── D-Dependency-Inversion/
│       ├── 02-Creational-Patterns/
│       │   ├── Singleton/
│       │   ├── Factory-Method/
│       │   └── Builder/
│       ├── 03-Structural-Patterns/
│       │   ├── Repository/
│       │   └── Decorator/
│       └── 04-Behavioral-Patterns/
│           ├── Observer/
│           ├── Strategy/
│           └── Chain-of-Responsibility/
│
└── 📄 README.md

🛠️ Tools & Environment

Tool	Version	Purpose
Visual Studio	2026	Primary IDE
.NET SDK	10.0	Runtime & tooling
C#	14	Language version
Git	Latest	Version control

🚀 How to Use This Repo

# 1. Clone the repository
git clone https://github.com/arvind01A/csharp-learning.git
cd csharp-learning

# 2. Navigate to any day
cd day1/01-Variables

# 3. Run any .cs file
dotnet script Program.cs
# or
dotnet run

🤝 Contributing & Feedback

Found a mistake? Have a better explanation?

⭐ Star this repo if it helped you
🐛 Open an issue for corrections or suggestions
🍴 Fork & PR if you'd like to contribute notes

🏁 10 Days · Complete C# Interview Roadmap

Made with ❤️ and ☕ by Arvind Kumar

"The best way to learn is to teach." — Keep pushing forward! 🚀

Name		Name	Last commit message	Last commit date
Latest commit History 132 Commits
ArrayApplication		ArrayApplication
Asyncprogramming		Asyncprogramming
Best Practices		Best Practices
Collections		Collections
Constructors		Constructors
ControlStatements		ControlStatements
DataTypes		DataTypes
Delegates		Delegates
Design Patterns		Design Patterns
EH		EH
Events		Events
Fields		Fields
FileHandling		FileHandling
Functional		Functional
Generic		Generic
MethodsParams		MethodsParams
Multithreading		Multithreading
OOPs		OOPs
Operators		Operators
Serialization		Serialization
StringApplication		StringApplication
TuplesApplication		TuplesApplication
Variables		Variables
loops		loops
.gitattributes		.gitattributes
.gitignore		.gitignore
README.md		README.md
csharp.slnx		csharp.slnx

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Latest commit

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🚀 C# Learning Journey

Day-by-Day Revision & Notes

🎉 Journey Completed!

📖 Overview

🎯 Roadmap — Completed ✅

📅 All 10 Days — Complete

📚 Day-by-Day Notes

🟣 Day 1 — Fundamentals

📦 Variables & Data Types

➕ Operators

🔀 Control Statements

🔁 Loops & Jump Statements

🔵 Day 2 — Classes & Objects

🏗️ Methods & Parameters

🏛️ Constructors

🗂️ Fields

🟢 Day 3 — OOP Pillars

🔒 Encapsulation · 🧬 Inheritance · 🎭 Abstraction · 🔄 Polymorphism

🟡 Day 4 — Basic Data Structures

🟠 Day 5 — Generics

🔷 Day 6 — Collections

🔴 Day 7 — Exception & File Handling

🟤 Day 8 — Expert I: Functional Programming & Delegates

⚡ Day 9 — Expert II: Multithreading, Async & Serialization

🏆 Day 10 — Expert III: Best Practices & Design Patterns

✅ C# Best Practices

📛 Naming Conventions

🧹 Clean Code Principles

🛡️ Null Safety (C# 8+)

🆕 Modern C# Features (C# 10–14)

🏗️ SOLID Principles

S — Single Responsibility

O — Open/Closed

L — Liskov Substitution

I — Interface Segregation

D — Dependency Inversion

🎨 Design Patterns

🏭 Singleton — one instance globally

🏭 Factory Method — decouple creation

🏭 Builder — step-by-step construction

🔧 Repository — abstract data access

🔧 Decorator — add behaviour without inheritance

🔁 Observer — notify subscribers

🔁 Strategy — swap algorithms at runtime

🔁 Chain of Responsibility — pipeline processing

🗂️ Repository Structure

🛠️ Tools & Environment

🚀 How to Use This Repo

🤝 Contributing & Feedback

🏁 10 Days · Complete C# Interview Roadmap

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