C # Cheat Sheet 📖 Microsoft OOP Language - Create Web / Desktop / Mobile / Game (Unity)

C # Cheat Sheet

📖 Introduction - What to understand before you start?

1.C # What is? - Microsoft OOP Language - Create Web / Desktop / Mobile / Game (Unity) - Run on .NET

2.Install / run where? - Install the .NET SDK → dotnet new console → dotnet run

3.Syntax BASIC - END WITH;, Very Java-like (race designed), comment - / / / * * /

4.Naming Convention - class / method / property PascalCase, parameter / local camelCase, interface Initial I (IUser)

5.Recommended Tools - IDE: Visual Studio (Windows), JetBrains Rider, VS Code + C # extension

📊 50 Codes to Know

🔹 Basics (1-5)

1. Hello World: Console.WriteLine ("Hello"); - Display text

2. Main Method: static void Main (string [] args) {...} - Beginning (C # 9 + Get top-level)

3.Namespace: namespace MyApp {....} - Group class

4. Using: Using System; - Import library

5.Input: string name = Console.ReadLine (); - get input

🔹 Data Types (6-10)

6.Variable: int age = 30; string name = "John"; - indicate type straight

7. VAR: VAR age = 30; - type inference

8. const / readonly: const int MAX = 100; readonly int x; - constant

9.Nullable: int? age = null; string? name = null; - null can be obtained.

10.Array: int [] arr = {1, 2, 3}; - fixed size

🔹 Operators (11-15)

11.Math: + - * /% + + - - plus minus times divided by moth

12.Comparison: = =! = > < > = < = - Compare (C # string use = = can!)

13.Logic: & & | |! - AND, OR, NOT

14.Null Coalesce: string s = x?? "default"; - default value if null

15.Null Conditional: user?. Name?. Length - no error if not

🔹 Control Flow (16-20)

16. If-else: if (x > 0) {...} else if {...} else {...} - Decide.

17.Ternary: string s = x > 0? "+": "-"; - if-else abbreviated

18.Switch Expressions: var s = x switch {1 = > "one," _ = > "other"}; - C # 8 +

19. For Loop: for (int i = 0; i < 10; i + +) {...} - loop

20. Foreach: foreach (var item in list) {...} - Loop Collection

🔹 Functions / Methods (21-25)

21.Method: public int add (int a, int b) = > a + b; - expression body

22. Default Param: void Greet (string name = "World") {...} - default

23. Named Args: Greet (name: "John"); - Name the name of the calling episode.

24. out / ref: bool TryParse (string s, out int result) - return multiple values

25.Lambda: Func < int, int > sq = x = > x * x; - Untitled

🔹 Collections / LINQ (26-30)

26.List: List < string > list = new () {"a," "b"}; - List scalable

27.Dictionary: Dictionary < string, int > d = new (); - key-value

28.HashSet: HashSet < int > s = new () {1, 2, 3}; - Unique Value

29.LINQ: List.Where (x = > x > 0) .Select (x = > x * 2) .ToList (); - Read SQL-likes

30.Tuple: var (a, b) = (1, 2); - return multiple values

🔹 OOP (31-35)

31. Class: Dog class {public string name {get; set;}} - auto property

32. Constructor: Public Dog (string name) {name = name;} - Create an instance

33. Inheritance: Puppy class: Dog {...} -: instead of extends

34. Interface: IAnimal interface {void Speak ();} - beginning I

35. Virtual / override: public virtual void Run () {} override void Run () {} - tracing method

🔹 Error Handling (36-40)

36. Try-Catch: Try {...} catch (Exception e) {...} - Trap error

37. Throw: throw new ArgumentException ("Wrong!"); - throw error.

38. Finally: try {...} catch {...} Finally {...} - Always do.

39. Using: using var file = new StreamReader ("f.txt"); - auto dispose

40. When Filter: catch (Exception e) when (e.HResult > 0) - catch filter

🔹 Async / Advanced (41-45)

41. Async / await: async Task < string > Get () {return await....;} - async work

42.Generic: class Box < T > {public T Value;} - type parameter

43.Enum: Enum Color {Red, Green, Blue} - Constant Set

44. Record (C # 9 +): Record Point (int X, int Y); - immutable data class

45. Pattern matching: if (obj is string s) {...} - check + convert type

🔹 Common Patterns (46-50)

46.String Interpolation: $"Hello {name}, age {age}" - Insert variable

47.StringBuilder: var sb = new StringBuilder (); sb.Append ("a"); - per string

48. DateTime: DateTime.Now; DateTime.Parse ("2026-01-01"); - Timer

49.JSON: JsonSerializer.Serialize (obj); Deserialize < T > (json); - object ↔ string

50.Sort: List.Sort (); List.OrderBy (x = > x.Age) .ToList (); - Sort

💡 Tips & Common Mistakes

- ⚠️ NullReferenceException - Mandatory?.???? = - Open nullable reference types in .csproj

- ⚠️ = = on object unsafe - override Equals () + GetHashCode () in customs class

- ⚠️ async void Danger - Catch error not! Use async Task except Event Handler

- ⚠️ Don't .Result / .Wait () on async - cause deadlock in UI thread

- 💡 Use LINQ instead for loop - Easy to read, good chain method

- 💡 record for DTO - immutable + value equality + auto getters

- 💡 Top-level statements (C # 9 +) - No need to write class Program {...Main (...)} Then - Short, Clean