Learn C#
five minutes at a time.

string name = "Pebble";
Console.WriteLine($"Hello, {name}!");

Hello, Pebble!

The Codiqo C# course starts at Console.WriteLine and covers variables, strings, conditions, loops, lists, methods, LINQ, classes and interfaces. Every example was compiled with warnings treated as errors.

How the C# lessons work

The full C# curriculum

1. Foundations

   Output, variables, types, input and logic.

   First Steps: Write your first C# programs.

   • Hello, C#: Print with Console.WriteLine
   • Variables and Types: Store values in int, double, bool, char and string
   • Arithmetic: Calculate with + - * / % and predict integer division
   • String Interpolation and Comments: Insert values into text with interpolated strings

   Text and Input: Work with strings and read input.

   • Strings: Join, measure and index text
   • String Methods: Use ToUpper, Trim, Substring, Contains and more
   • Reading Input: Read lines with Console.ReadLine and convert them
   • Project: Tip Calculator: Calculate and format a bill split

   Logic: Make true or false decisions.

   • Comparisons and bool: Compare values and store booleans
   • Logical Operators: Combine conditions with && || and !
   • Conversions and Math: Convert safely with TryParse and use the Math class
   • Project: Eligibility Checker: Decide eligibility from several conditions

2. Control Flow

   Decisions, loops and methods.

   Making Decisions: Run different code depending on conditions.

   • if and else: Run code only when a condition is true
   • else if and Nesting: Choose between several paths
   • switch and Switch Expressions: Match values with switch
   • Project: Grade Calculator: Turn scores into grades

   Loops: Repeat work with while, for and foreach.

   • while and do-while: Repeat while a condition is true
   • for Loops: Count with for and nest loops
   • foreach, break and continue: Visit every item and control loops
   • Project: FizzBuzz: Solve the classic FizzBuzz problem

   Methods: Reuse code with methods.

   • Defining Methods: Write and call static methods
   • Parameters and Return Values: Use optional and named arguments
   • ref, out and Scope: Return several results and understand local variables
   • Project: Temperature Converter: Build a converter from small methods

3. Data and LINQ

   Arrays, lists, dictionaries and queries.

   Arrays and Lists: Store and change collections of values.

   • Arrays: Create arrays and read and change items
   • List<T>: Grow and shrink lists
   • Looping and Searching: Find, count and check items
   • Project: To-Do List: Manage a list of tasks

   Dictionaries and LINQ: Look up by key and query data.

   • Dictionary: Store and look up key-value pairs
   • LINQ: Where and Select: Filter and transform collections
   • LINQ: Order, Sum and Group: Sort, total and group data
   • Project: Grade Statistics: Summarise a class's scores

   Text and Null Safety: Build text and handle missing values.

   • StringBuilder and Formatting: Build text and format numbers
   • Split and Join: Break text apart and put it back together
   • Nullable Types: Handle missing values with ?, ?? and ?.
   • Project: Word Counter: Count the words in a piece of text

4. Object-Oriented C#

   Classes, inheritance, interfaces, errors and a complete project.

   Classes and Objects: Model things with your own classes.

   • Classes and Objects: Define a class and create objects
   • Constructors and Properties: Initialise objects and expose data with properties
   • Encapsulation: Protect state with private fields and validation
   • Project: Bank Account: Model an account with safe deposits and withdrawals

   Inheritance and Interfaces: Share behaviour and handle problems.

   • Inheritance: Extend classes and override methods
   • Interfaces and Polymorphism: Program to an interface
   • Exceptions: Throw and catch exceptions
   • Project: Shapes: Compute areas through a shared interface

   Capstone Project: Plan and build a complete C# program.

   • Planning and Modelling: Turn an idea into classes and records
   • Core Logic: Implement the main features
   • Errors and Testing: Handle bad input and check behaviour
   • Polishing: Improve output, structure and readability

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