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C#: From Fundamentals to Advanced Techniques - A Beginner-Friendly CheatSheet

by Sukhpinder SinghMarch 24th, 2024

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The comprehensive C# Cheat Sheet is designed to aid developers in mastering key syntax and concepts related to C# programming.

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The comprehensive C# Cheat Sheet is designed to aid developers in mastering key syntax and concepts related to C# programming.

Basic Structure
Data Types
Variables
Constants
Conditional Statements
Loops
Arrays
Lists
Dictionaries
Methods
Classes & Objects
Exception Handling
Delegates, Events & Lambdas
LINQ (Language-Integrated Query)
Attributes
Async/Await
Miscellaneous
String Manipulation
File I/O
Date & Time
Generics
Nullables
Attributes & Reflection
Extension Methods
Dependency Injection
Partial Classes
Interoperability
Anonymous Types
Tuples
Pattern Matching
Local Functions
Records
with Expressions
Indexers and Ranges
using Declaration
Nullable Reference Types (NRTs)
Pattern-Based Using
Property Patterns
Default Interface Implementations
Dynamic Binding

1. Basic Structure

All C# programs follow a fundamental structure, outlined below:

    using System;
    
    public class HelloWorld
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");
        }
    }

Starting with .NET 5, top-level statements simplify the Program.cs content:

    Console.WriteLine("Hello, World");

2. Data Types

C# supports various data types such as:

Value Types: int, char, and float
Reference Types: string, class, and array

3. Variables

Variables are symbolic names for values:

    int age = 30; // integer variable
    string name = "John"; // string variable
    double PI = 3.14159; // double for floating-point numbers
    bool isLoggedIn = true; // boolean variable

Use ‘var’ for type inference:

    var number = 5; // compiler infers type as int
    var message = "This is a message"; // compiler infers type as string

4. Constants

Constants hold immutable values:

    const double GRAVITY = 9.81; // constant for gravitational acceleration
    const string COMPANY_NAME = "MyCompany"; // constant company name

5. Conditional Statements

Control program flow based on conditions:

    int age = 20;
    
    if (age >= 18)
    {
        Console.WriteLine("You are eligible to vote.");
    }
    else
    {
        Console.WriteLine("You are not eligible to vote.");
    }
    
    switch (variable) { /*...*/ } // Switch statement

6. Loops

Execute code repeatedly:

    for (int i = 1; i <= 5; i++)
    {
        Console.WriteLine(i);
    }
    
    foreach (var item in collection) { /*...*/ } // Foreach loop
    
    while (condition) { /*...*/ } // While loop
    
    do { /*...*/ } while (condition); // Do-while loop

7. Arrays

Fixed-size collections of elements:

    string[] names = new string[3] { "Alice", "Bob", "Charlie" };
    Console.WriteLine(names[1]); // Output: Bob (accessing element at index 1)

8. Lists

Dynamic collections similar to arrays:

    List<int> numbers = new List<int>();
    numbers.Add(1);
    numbers.Add(2);
    numbers.Add(3);
    
    foreach (var number in numbers)
    {
        Console.WriteLine(number);
    }

9. Dictionaries

Key-value pairs for data association:

    Dictionary<string, string> phonebook = new Dictionary<string, string>();
    phonebook.Add("John Doe", "123-456-7890");
    phonebook.Add("Jane Doe", "987-654-3210");
    
    Console.WriteLine(phonebook["John Doe"]); // Output: 123-456-7890

10. Methods

Encapsulate reusable logic:

    public class Rectangle
    {
        public double Width { get; set; }
        public double Height { get; set; }
    
        public double GetArea()
        {
            return Width * Height;
        }
    }
    
    public class Program
    {
        public static void Main(string[] args)
        {
            Rectangle rect = new Rectangle();
            rect.Width = 5;
            rect.Height = 10;
    
            double area = rect.GetArea();
            Console.WriteLine($"Area of rectangle: {area}");
        }
    }

11. Classes & Objects

Classes define blueprints for objects:

    public class MyClass // Class definition
    {
        public string PropertyName { get; set; } // Properties store data
        public void MethodName() { /*...*/ } // Methods define actions
    }
    
    MyClass obj = new MyClass(); // Object creation

12. Exception Handling

Manage runtime errors gracefully:

    public static int GetNumberInput()
    {
      while (true)
      {
        try
        {
          Console.WriteLine("Enter a number: ");
          string input = Console.ReadLine();
          return int.Parse(input);
        }
        catch (FormatException)
        {
          Console.WriteLine("Invalid input. Please enter a number.");
        }
      }
    }
    
    public static void Main(string[] args)
    {
      int number = GetNumberInput();
      Console.WriteLine($"You entered: {number}");
    }

13. Delegates, Events & Lambda

For event-driven programming and method handling:

    public delegate void MyDelegate(); // Delegate declaration
    
    event MyDelegate MyEvent; // Event declaration
    
    public class Person
    {
      public string Name { get; set; }
      public int Age { get; set; }
    }
    
    public static void Main(string[] args)
    {
      List<Person> people = new List<Person>()
      {
        new Person { Name = "Alice", Age = 30 },
        new Person { Name = "Bob", Age = 25 },
        new Person { Name = "Charlie", Age = 40 },
      };
    
      people.Sort((p1, p2) => p1.Name.CompareTo(p2.Name));
    
      foreach (var person in people)
      {
        Console.WriteLine(person.Name); // Output: Alice, Bob, Charlie (sorted by name)
      }
    }

14. LINQ (Language-Integrated Query)

Query capabilities for data manipulation:

    using System.Linq;
    
    public static void Main(string[] args)
    {
      List<int> numbers = new List<int>() { 1, 2, 3, 4, 5, 6 };
      var evenNumbers = numbers.Where(x => x % 2 == 0);
    
      foreach (var number in evenNumbers)
      {
        Console.WriteLine(number); // Output: 2, 4, 6
      }
    }

15. Attributes

Add metadata to code elements:

    [Obsolete("Use the new DoSomethingV2 method instead.")]
    public void DoSomething()
    {
      // Implementation here
    }
    
    public void DoSomethingV2()
    {
      // New and improved implementation
    }

16. Async/Await

For non-blocking code execution:

    using System.Threading.Tasks;
    
    public static async Task DownloadFileAsync(string url, string filePath)
    {
      // Simulate downloading data asynchronously
      await Task.Delay(2000); // Simulate a 2-second download
    
      // Write downloaded data to the file
      File.WriteAllText(filePath, "Downloaded content");
      Console.WriteLine($"File downloaded to: {filePath}");
    }
    
    public static void Main(string[] args)
    {
      string url = "https://example.com/data.txt";
      string filePath = "downloaded_data.txt";
    
      DownloadFileAsync(url, filePath);
    
      // Continue program execution while download happens in the background
      Console.WriteLine("Downloading file...");
      Console.WriteLine("Meanwhile, you can do other things...");
    }

17. Miscellaneous

Additional language features:

enum, interface, class, record, and struct

dynamic, is, as, var, and nameof

18. String Manipulation

Powerful string handling methods:

    string.Concat(); // Combine strings
    string.Join(); // Join elements
    str.Split(); // Split string
    str.ToUpper(); // Convert to uppercase
    str.ToLower(); // Convert to lowercase

19. File I/O

Operations with files:

    using System.IO; // Required for File I/O
    
    File.ReadAllText(path); // Read file content
    File.WriteAllText(path, content); // Write to file
    File.Exists(path); // Check file existence

20. Date & Time

Date and time manipulation:

    using System;
    
    public static void Main(string[] args)
    {
      DateTime startDate = DateTime.Parse("2024-03-10");
      DateTime endDate = DateTime.Now;
    
      TimeSpan difference = endDate - startDate;
      Console.WriteLine($"Time difference: {difference.Days} days, {difference.Hours} hours");
    }

21. Generics

Type-safe data structures:

    public class Stack<T>
    {
      private List<T> items = new List<T>();
    
      public void Push(T item)
      {
        items.Add(item);
      }
    
      public T Pop()
      {
        T item = items[items.Count - 1];
        items.RemoveAt(items.Count - 1);
        return item;
      }
    }
    
    public static void Main(string[] args)
    {
      Stack<string> messages = new Stack<string>();
      messages.Push("Hello");
      messages.Push("World");
    
      string message = messages.Pop();
      Console.WriteLine(message); // Output: World
    }

22. Nullables

Allow value types to be null:

    int? nullableInt = null; // Nullable integer

23. Attributes & Reflection

Metadata and type introspection:

    public class Person
    {
      public string Name { get; set; }
      public int Age { get; set; }
    }
    
    public static void Main(string[] args)
    {
      Type personType = typeof(Person);
      PropertyInfo[] properties = personType.GetProperties();
    
      foreach (PropertyInfo property in properties)
      {
        Console.WriteLine(property.Name); // Output: Name, Age
      }
    }

24. Extension Methods

Add methods to existing types:

    public static class StringExtensions
    {
      public static string ToUppercase(this string str)
      {
        return str.ToUpper();
      }
    }
    
    public static void Main(string[] args)
    {
      string message = "Hello, world!";
      string uppercased = message.ToUppercase(); // Using the extension method
      Console.WriteLine(uppercased); // Output: HELLO, WORLD!
    }

25. Dependency Injection

Loosely coupled code design:

    public interface ILogger
    {
      void LogMessage(string message);
    }
    
    public class MyService
    {
      private readonly ILogger _logger;
    
      public MyService(ILogger logger)
      {
        _logger = logger;
      }
    
      public void DoSomething()
      {
        _logger.LogMessage("Doing something...");
      }
    }
    
    // Implementing the ILogger interface (example)
    public class ConsoleLogger : ILogger
    {
      public void LogMessage(string message)
      {
        Console.WriteLine(message);
      }
    }
    
    public static void Main(string[] args)
    {
      ILogger logger = new ConsoleLogger();
      MyService service = new MyService(logger);
      service.DoSomething();
    }

26. Partial Classes

Splitting a single class definition:

    public partial class MyClass { /*...*/ } // Partial class definition

27. Interoperability

Interop with other languages:

    using System;
    using System.Runtime.InteropServices;
    
    [DllImport("user32.dll")]
    public static extern int MessageBox(IntPtr hWnd, string lpText, string lpCaption, uint uType);
    
    public static void Main(string[] args)
    {
      MessageBox(IntPtr.Zero, "Hello from C#!", "Interop Example", 0);
    }

28. Anonymous Types

Creating unnamed types:csharpCopy code

    var person = new { Name = "John", Age = 30 };
    Console.WriteLine($"Name: {person.Name}, Age: {person.Age}");

29. Tuple

Data structures with a specific number of elements:

    (string Name, int Age) person = ("Alice", 30);
    Console.WriteLine($"Name: {person.Name}, Age: {person.Age}"); // Accessing elements using Item1 and Item2

30. Pattern Matching

Simplifies certain programming tasks:

    object obj = new Person { Name = "Bob", Age = 25 };
    
    if (obj is Person { Name: "Bob", Age >= 18 })
    {
      Console.WriteLine("Bob is an adult.");
    }

31. Local Functions

Encapsulate logic within methods:

    public static int Calculate(int number)
    {
      int Factorial(int n)
      {
        if (n == 0) return 1;
        return n * Factorial(n - 1);
      }
    
      return Factorial(number);
    }
    
    public static void Main(string[] args)
    {
      int result = Calculate(5);
      Console.WriteLine($"5! = {result}");
    }

32. Records

Concise syntax for reference types:

    public record Person(string Name, int Age);
    
    public static void Main(string[] args)
    {
      Person person1 = new Person("Alice", 30);
      Person person2 = new Person("Alice", 30);
    
      // Records provide default equality comparison
      if (person1 == person2)
      {
        Console.WriteLine("People are equal");
      }
    }

33. with Expressions

Non-destructive mutation for records:

    var john = new Person("John", 30);
    var jane = john with { Name = "Jane" }; // Non-destructive mutation

34. Indexers and Ranges

Flexible data access:

    int[] arr = {0, 1, 2, 3, 4, 5};
    var subset = arr[1..^1]; // Indexer and range usage

35. using Declaration

Dispose of IDisposable objects:

    using var reader = new StreamReader("file.txt"); // using declaration

36. Nullable Reference Types (NRTs)

Avoid null reference exceptions:

    public class Person
    {
      public string Name { get; set; }
      public int Age { get; set; }
    }
    
    public static void Main(string[] args)
    {
      Person person = new Person() { Age = 30 };
    
      // NRTs require null checks before accessing properties
      if (person?.Name != null)
      {
        Console.WriteLine(person.Name);
      }
      else
      {
        Console.WriteLine("Name is null");
      }
    }

37. Pattern-Based Using

More patterns in the using statement:

    public ref struct ResourceWrapper { /*...*/ } // Resource wrapper
    
    using var resource = new ResourceWrapper(); // Pattern-based using

38. Property Patterns

Deconstruct objects in pattern matching:

    if (obj is Person { Name: "John", Age: var age }) { /*...*/ } // Property pattern matching

39. Default Interface Implementations

Interfaces with default method implementations:

    public interface IPerson { /*...*/ } // Interface with default method
    public class MyClass : IPerson { /*...*/ } // Class implementing interface

40. Dynamic Binding

Runtime type resolution:

    dynamic d = 5; // Dynamic binding
    d = "Hello"; // No compile-time type checking

Conclusion

This structured C# Cheat Sheet concludes with advanced topics and techniques, providing a comprehensive reference for developers aiming to enhance their C# programming skills. For detailed examples and further exploration, refer to the specific sections outlined in this guide. Happy coding!