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

The comprehensive C# Cheat Sheet is designed to aid developers in mastering key syntax and concepts related to C# programming. Contents 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 numbers = new List (); 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 phonebook = new Dictionary (); 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 people = new List () { 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 numbers = new List () { 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 { private List items = new List (); 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 messages = new Stack (); 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! C# Programming🚀 Thank you for being a part of the C# community! Before you leave: If you’ve made it this far, please show your appreciation with a clap, and follow the author! 👏️️ Follow us: | | | | | X LinkedIn Dev.to Hashnode Newsletter Tumblr Visit our other platforms: | | | | GitHub Instagram Tiktok Quora Daily.dev Inspired By: https://zerotomastery.io/cheatsheets/csharp-cheat-sheet/#constants Also published here