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Learn C#

A free, interactive online C# course. You write C# on every lesson — syntax, classes, inheritance, interfaces, LINQ — with real C# code examples, AI hints when you're stuck, and a free certificate of completion when you finish.

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  • Beginner friendly
  • sparkles iconAI-assisted coding help
  • hint iconHands-on interactive lessons
  • volume On iconAudio narration on every lesson
  • quiz iconQuizzes to test your knowledge
  • certificate iconFree certificate of completion

Syllabus

3 sections3 projects205 lessons185 challenges1,295 quiz questions
  1. Section 1

    Fundamentals

    Start sectionStartExpandCollapse    Build a strong foundation with essential concepts and basic skills69 lessons62 challenges410 questions1 project

    Introduction

    4 lessons323
    • 01C#Challenge
    • 02Hello World!ChallengeQuiz
    • 03CommentsQuiz
    • 04Basic Program StructureChallengeQuiz

    Variables Part 1

    5 lessons539
    • 01NumbersChallengeQuiz
    • 02CharChallengeQuiz
    • 03StringChallengeQuiz
    • 04BooleanChallengeQuiz
    • 05Type DeclarationChallengeQuiz

    Variables Part 2

    5 lessons431
    • 01VarChallengeQuiz
    • 02ConstantsChallengeQuiz
    • 03Naming ConventionsQuiz
    • 04Recap - Initialize VariablesChallenge
    • 05Type CastingChallengeQuiz

    Operators Part 1

    5 lessons438
    • 01Arithmetic OperatorsChallengeQuiz
    • 02Modulo OperatorChallengeQuiz
    • 03Increment/DecrementChallengeQuiz
    • 04Post Increment/DecrementQuiz
    • 05Arithmetic ShortcutsChallengeQuiz

    Operators Part 2

    5 lessons531
    • 01Comparison OperatorsChallengeQuiz
    • 02Logical Operators Part 1ChallengeQuiz
    • 03Logical Operators Part 2ChallengeQuiz
    • 04Recap - Simple LogicChallenge
    • 05Logical Operators Part 3ChallengeQuiz

    Decision Making

    6 lessons638
    • 01If StatementChallengeQuiz
    • 02If - ElseChallengeQuiz
    • 03Switch StatementChallengeQuiz
    • 04Ternary OperatorChallengeQuiz
    • 05Recap - If ElseChallenge
    • 06Nested If - ElseChallengeQuiz

    Basic IO

    6 lessons633
    • 01Basic OutputChallengeQuiz
    • 02String InterpolationChallengeQuiz
    • 03Reading InputChallengeQuiz
    • 04ParseChallengeQuiz
    • 05Recap - Till 120Challenge
    • 06Recap - True or FalseChallenge

    Calculator App

    Project4 lessons1
    • 01Welcome MessageChallenge
    • 02Getting NumbersProject
    • 03Basic OperationsProject
    • 04Formatted OutputProject

    Loops

    8 lessons752
    • 01For LoopChallengeQuiz
    • 02While LoopChallengeQuiz
    • 03Do While LoopChallengeQuiz
    • 04BreakChallengeQuiz
    • 05ContinueChallengeQuiz
    • 06Nested LoopChallengeQuiz
    • 07Infinite LoopQuiz
    • 08Recap - Dynamic InputChallenge

    Methods (Functions)

    6 lessons641
    • 01Declaring MethodsChallengeQuiz
    • 02Method ParametersChallengeQuiz
    • 03Return TypesChallengeQuiz
    • 04Optional ParametersChallengeQuiz
    • 05Recap - Validation FunctionChallenge
    • 06Void MethodsChallengeQuiz

    Arrays Basics

    6 lessons629
    • 01Declaring ArraysChallengeQuiz
    • 02Accessing ElementsChallengeQuiz
    • 03Modifying ArraysChallengeQuiz
    • 04Array MethodsChallengeQuiz
    • 05Recap - Product ArrayChallenge
    • 06Edit Recap - Reversed ArrayChallenge

    String Operations

    3 lessons324
    • 01String Methods Part 1ChallengeQuiz
    • 02String Methods Part 2ChallengeQuiz
    • 03String FormattingChallengeQuiz

    Iterating Over Collections

    3 lessons323
    • 01Using For LoopChallengeQuiz
    • 02Foreach LoopChallengeQuiz
    • 03Common Array OperationsChallengeQuiz

    Final Challenges

    3 lessons38
    • 01Number PatternChallengeQuiz
    • 02Pattern FinderChallenge
    • 03Student Grade CalculatorChallenge
  2. Section 2

    Logic & Flow

    Start sectionStartExpandCollapse    Master advanced C# programming with a focus on data structures and flow control. Learn to work with complex arrays, collections, error handling, and time management.66 lessons77 challenges394 questions1 project

    Multi-dimensional Arrays

    7 lessons750
    • 012D Arrays BasicsChallengeQuiz
    • 02Declaring and Initializing 2DQuiz
    • 03Accessing 2D Array ElementsChallengeQuiz
    • 04Nested Loops with 2D ArraysChallengeQuiz
    • 05Jagged ArraysChallengeQuiz
    • 06Common Matrix OperationsChallengeMasteryQuiz
    • 07Recap - Multi-dimensionalChallenge

    Advanced Decision Making

    5 lessons932
    • 01Multiple ConditionsChallengeMasteryQuiz
    • 02Complex Boolean LogicChallengeMasteryQuiz
    • 03If vs. Switch ComparisonChallengeMasteryQuiz
    • 04Nested Switch StatementsChallengeMasteryQuiz
    • 05Recap - Advanced DecisionsChallenge

    Loop Enhancements

    5 lessons632
    • 01Loop PerformanceChallengeQuiz
    • 02Iterating ComplexChallengeQuiz
    • 03Each Loop TypeChallengeMasteryQuiz
    • 04Refactoring LoopsChallengeQuiz
    • 05Recap - Optimized LoopsChallenge

    Flow Control Techniques

    5 lessons938
    • 01Early ReturnsChallengeQuiz
    • 02Guard ClausesChallengeMasteryQuiz
    • 03Jump Statements (goto)ChallengeMasteryQuiz
    • 04Break and ContinueChallengeMasteryQuiz
    • 05Flatten Nested ConditionalsChallengeMasteryQuiz

    Exception Handling

    8 lessons1160
    • 01Try-Catch BasicsChallengeMasteryQuiz
    • 02Exception TypesChallengeQuiz
    • 03Multiple Catch BlocksChallengeMasteryQuiz
    • 04Working with FilesChallengeQuiz
    • 05Finally BlockChallengeMasteryQuiz
    • 06Using vs. Try-FinallyChallengeQuiz
    • 07Custom ExceptionsChallengeQuiz
    • 08Recap - Error HandlingChallenge

    Null Handling

    5 lessons832
    • 01Null Reference BasicsChallengeMasteryQuiz
    • 02Nullable Value TypesChallengeQuiz
    • 03Null Checking PatternsChallengeMasteryQuiz
    • 04Defensive ProgrammingChallengeMasteryQuiz
    • 05Recap - Null SafetyChallenge

    Logical Operators Advanced

    4 lessons723
    • 01Short-Circuit EvaluationChallengeMasteryQuiz
    • 02Conditional Logical OperatorsChallengeMasteryQuiz
    • 03Operator PrecedenceChallengeMasteryQuiz
    • 04Recap - Advanced OperatorsChallenge

    Data Analysis System

    Project6 lessons1
    • 01Data Collection SetupChallenge
    • 02Data Entry LogicProject
    • 03Data AnalysisProject
    • 04Grading LogicProject
    • 05Report GenerationProject
    • 06 Error HandlingProject

    HashMap Part 1

    6 lessons536
    • 01What is a HashMap?Quiz
    • 02Declare a HashMapChallengeQuiz
    • 03Check If Key ExistsChallengeQuiz
    • 04Accessing ValuesChallengeQuiz
    • 05Modifying DictionariesChallengeQuiz
    • 06Recap - HashMapChallenge

    HashMap Part 2

    4 lessons415
    • 01HashMap MethodsChallengeQuiz
    • 02Nested HashMapChallengeQuiz
    • 03Recap - Manage WarehouseChallenge
    • 04Recap - HashMap OperationsChallenge

    HashSet Part 1

    6 lessons537
    • 01What is a HashSet?Quiz
    • 02Adding an ElementChallengeQuiz
    • 03Removing an ElementChallengeQuiz
    • 04Checking if an Element ExistsChallengeQuiz
    • 05Empty and SizeChallengeQuiz
    • 06Recap - HashSetChallenge

    HashSet Part 2

    5 lessons539
    • 01Math - Union of HashSetsChallengeQuiz
    • 02Math - Intersection of HashSetChallengeQuiz
    • 03Math - Set DifferenceChallengeQuiz
    • 04Math - Symmetric DifferenceChallengeQuiz
    • 05Iterating Over SetsChallengeQuiz
  3. Section 3

    Object Oriented Programming

    Start sectionStartExpandCollapse    Discover how to organize code with classes, objects, and reusable structures70 lessons65 challenges491 questions1 project

    Fundamentals of OOP

    9 lessons972
    • 01External FilesChallengeQuiz
    • 02Namespaces & DirectivesChallengeQuiz
    • 03Intro to Classes & ObjectsChallengeQuiz
    • 04The 'this' KeywordChallengeQuiz
    • 05Methods and ParametersChallengeQuiz
    • 06Fields vs PropertiesChallengeQuiz
    • 07ConstructorsChallengeQuiz
    • 08Object InitializersChallengeQuiz
    • 09Recap - Simple CalculatorChallenge

    Properties & Static Members

    5 lessons545
    • 01Auto-Implemented PropertiesChallengeQuiz
    • 02Read/Write-Only PropertiesChallengeQuiz
    • 03Static Fields & MethodsChallengeQuiz
    • 04Static ClassesChallengeQuiz
    • 05Expression-Bodied MembersChallengeQuiz

    Class Architecture

    4 lessons427
    • 01Instance vs Static DataChallengeQuiz
    • 02'readonly' & 'const' KeywordsChallengeQuiz
    • 03Backing FieldsChallengeQuiz
    • 04Recap - Bank Account ManagerChallenge

    Inheritance

    6 lessons644
    • 01Basic Inheritance (:) SyntaxChallengeQuiz
    • 02The 'base' KeywordChallengeQuiz
    • 03Virtual & Override KeywordsChallengeQuiz
    • 04Sealed ClassesChallengeQuiz
    • 05The 'object' Base ClassChallengeQuiz
    • 06Recap - Employee HierarchyChallenge

    Polymorphism & Interfaces

    6 lessons644
    • 01Compile vs Runtime PolyChallengeQuiz
    • 02Interface vs Abstract ClassChallengeQuiz
    • 03Multiple InterfacesChallengeQuiz
    • 04Explicit InterfacesChallengeQuiz
    • 05Upcasting & DowncastingChallengeQuiz
    • 06Recap - Shape CalculatorChallenge

    Encapsulation

    5 lessons535
    • 01Access ModifiersChallengeQuiz
    • 02Properties for EncapsulationChallengeQuiz
    • 03Data Hiding ImplementationChallengeQuiz
    • 04Immutability PatternsChallengeQuiz
    • 05Recap - Student RecordsChallenge

    Advanced Features

    5 lessons535
    • 01Operator OverloadingChallengeQuiz
    • 02Indexers (this[])ChallengeQuiz
    • 03ToString() OverrideChallengeQuiz
    • 04Extension MethodsChallengeQuiz
    • 05Recap - Custom ListChallenge

    Advanced OOP Concepts

    6 lessons653
    • 01Composition over InheritanceChallengeQuiz
    • 02Generics (Classes & Methods)ChallengeQuiz
    • 03Delegates and EventsChallengeQuiz
    • 04Attributes and ReflectionChallengeQuiz
    • 05IDisposable & using StatementChallengeQuiz
    • 06Dependency Injection BasicsChallengeQuiz

    Variable Arguments

    4 lessons436
    • 01The 'params' KeywordChallengeQuiz
    • 02Optional ParametersChallengeQuiz
    • 03Named ArgumentsChallengeQuiz
    • 04Method OverloadingChallengeQuiz

    Design Patterns Part 1

    5 lessons545
    • 01Intro to Design PatternsChallengeQuiz
    • 02Thread-Safe SingletonChallengeQuiz
    • 03Factory PatternChallengeQuiz
    • 04Observer Pattern (Events)ChallengeQuiz
    • 05Strategy PatternChallengeQuiz

    Design Patterns Part 2

    6 lessons655
    • 01Command PatternChallengeQuiz
    • 02Adapter PatternChallengeQuiz
    • 03Decorator PatternChallengeQuiz
    • 04Template Method PatternChallengeQuiz
    • 05State PatternChallengeQuiz
    • 06Composite PatternChallengeQuiz

    Project: Library System

    Project6 lessons1
    • 01Project StructureChallenge
    • 02Book and User ModelsProject
    • 03Borrowing System LogicProject
    • 04LINQ for SearchingProject
    • 05Console UI / Admin InterfaceProject
    • 06Unit Testing (NUnit/xUnit)Project

    Final Challenges

    3 lessons3
    • 01E-learning PlatformChallenge
    • 02Game Character ComponentChallenge
    • 03Vehicle Rental ServiceChallenge

Why learn C# with Coddy

  • Write and run real C# code in your browser. No Visual Studio install, no .NET SDK setup. Each lesson compiles your C# program server-side and shows the output instantly.
  • Object-oriented C# the way it's used in production: classes, properties, inheritance, interfaces, generics, exception handling, LINQ. Code examples and exercises after every concept.
  • AI hints help you debug C# code and read compiler errors so the language feels approachable instead of intimidating, especially if you're new to OOP.
  • Free C# certificate of completion when you finish. Useful for game-dev (Unity), backend, and enterprise roles where C# fluency is a baseline expectation.

Frequently asked questions about learning C#

Is C# hard to learn?

C# is one of the more approachable strongly-typed languages. The syntax is consistent, the standard library is large and well-documented, and modern features like properties and pattern matching cut down on boilerplate. Most beginners get their first C# program running within the first hour and reach classes and inheritance within a week.

How long does it take to learn C#?

C# basics — syntax, methods, classes, objects — take two to four weeks of daily practice. Comfortable use of inheritance, interfaces, generics, and LINQ usually takes one to three months. Going deeper into ASP.NET, Unity game development, or enterprise patterns is a separate ramp.

What's the difference between C# and Java?

C# and Java are close cousins. Both are strongly-typed, class-based, garbage-collected. C# tends to adopt new features faster (properties, LINQ, async/await, pattern matching) and is heavily used for Unity game development and Windows tooling. Java leans more toward Android and large enterprise backends. The skills transfer in both directions.

Can I use C# for game development?

Yes. C# is the primary scripting language for Unity, one of the most popular game engines in the world. The OOP fundamentals you'll pick up here (classes, inheritance, interfaces) map directly to Unity's component model, so finishing the C# course gives you a real head start on Unity.

Can I learn C# online for free?

Yes. The interactive C# course is free — lessons, coding exercises, quizzes, and a certificate. The editor runs in your browser so you don't need to install Visual Studio, the .NET SDK, or any IDE to start writing C#.

Do I get a C# certificate after the course?

Yes. Finishing the C# course gives you a free certificate of completion you can add to your resume or share on LinkedIn — a verifiable signal alongside any Unity projects, .NET apps, or GitHub repos you've built.
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