C# Cheat Sheet
Last updated
Hello World & program structure
Top-level statements (since .NET 6) let you skip the boilerplate class.
| Element | Code |
|---|---|
| Top-level program | Console.WriteLine("Hello, World!"); |
| Import a namespace | using System; |
| Classic entry point | static void Main(string[] args) { ... } |
| Print a line | Console.WriteLine("text"); |
| Read a line | string s = Console.ReadLine(); |
| String interpolation | Console.WriteLine($"Hi {name}"); |
| Comments | // line and /* block */ |
Data types
| Type | Description |
|---|---|
int | 32-bit signed integer |
long | 64-bit signed integer |
double / float | Floating point numbers |
decimal | High-precision decimal (money) |
bool | true or false |
char | Single Unicode character |
string | Immutable text |
var | Compiler infers the type |
int? | Nullable value type |
Variables
| Operation | Syntax |
|---|---|
| Declare & initialize | int x = 5; |
| Type inference | var name = "Ada"; |
| Constant | const double Pi = 3.14159; |
| Read-only field | readonly int id; |
| Nullable reference | string? maybe = null; |
| Null-coalescing | var y = maybe ?? "default"; |
| Null-conditional | int? len = text?.Length; |
Control flow
| Statement | Syntax |
|---|---|
| If / else | if (x > 0) { ... } else { ... } |
| Switch statement | switch (n) { case 1: ...; break; default: ...; } |
| Switch expression | var s = n switch { 1 => "one", _ => "other" }; |
| While loop | while (i < n) { ... } |
| Do-while loop | do { ... } while (i < n); |
| For loop | for (int i = 0; i < n; i++) { ... } |
| Foreach loop | foreach (var item in list) { ... } |
| Break / continue | break; exits a loop, continue; skips to next iteration |
Methods
| Operation | Syntax |
|---|---|
| Define a method | int Add(int a, int b) { return a + b; } |
| Expression-bodied | int Add(int a, int b) => a + b; |
| No return value | void Greet() { ... } |
| Optional parameter | int Pow(int b, int e = 2) { ... } |
| Named arguments | Pow(b: 2, e: 3); |
| Out parameter | bool TryParse(string s, out int n) { ... } |
| Static method | static int Square(int x) => x * x; |
| Lambda expression | Func<int, int> f = x => x * 2; |
Classes & OOP
| Operation | Syntax |
|---|---|
| Define a class | class Dog { ... } |
| Auto property | public string Name { get; set; } |
| Read-only property | public int Id { get; } |
| Constructor | public Dog(string name) { Name = name; } |
| Create an object | var d = new Dog("Rex"); |
| Inheritance | class Puppy : Dog { ... } |
| Interface | interface IRunnable { void Run(); } |
| Override a method | public override void Speak() { ... } |
| Record (immutable) | record Point(int X, int Y); |
Collections
Generic collections from System.Collections.Generic.
| Type | Use & example |
|---|---|
List<T> | Dynamic array: list.Add(1); list.Count; |
Dictionary<K, V> | Key-value: dict["a"] = 1; dict.ContainsKey("a"); |
HashSet<T> | Unique values: set.Add(5); set.Contains(5); |
Queue<T> | FIFO: q.Enqueue(x); q.Dequeue(); |
Stack<T> | LIFO: s.Push(x); s.Pop(); |
| Array | int[] nums = { 1, 2, 3 }; |
| Collection initializer | var l = new List<int> { 1, 2, 3 }; |
| Iterate a dictionary | foreach (var kv in dict) { kv.Key; kv.Value; } |
LINQ
Query collections fluently; from System.Linq.
| Operation | Syntax |
|---|---|
| Filter | nums.Where(n => n > 0) |
| Project / map | nums.Select(n => n * 2) |
| Sort | nums.OrderBy(n => n) / OrderByDescending(...) |
| First match | nums.First(n => n > 5) / FirstOrDefault(...) |
| Any / all | nums.Any(n => n < 0) / nums.All(n => n > 0) |
| Count matches | nums.Count(n => n > 0) |
| Aggregate | nums.Sum(), nums.Max(), nums.Average() |
| Group by | items.GroupBy(i => i.Category) |
| Materialize | .ToList() / .ToArray() |
Common patterns (properties, async)
| Pattern | Syntax |
|---|---|
| Async method | async Task<int> GetAsync() { ... } |
| Await a task | var result = await GetAsync(); |
| Try / catch | try { ... } catch (Exception e) { ... } |
| Finally | finally { ... } always runs |
| Using (dispose) | using var file = File.OpenRead(path); |
| String formatting | $"Total: {amount:C}" |
| Generic class | class Box<T> { public T Value; } |
| Pattern matching | if (obj is Dog d) { d.Bark(); } |
The C# syntax, collections, and LINQ queries you reach for most, on one page. This C# cheat sheet is a quick reference for writing C# - the data types, control flow, classes, the List/Dictionary collections, LINQ, and the property and async patterns that define idiomatic .NET code.
Everything here is standard C# on .NET and runs with the dotnet CLI. Copy what you need, or try any snippet live in the C# playground - no SDK to install.
C# cheat sheet FAQ
Is this C# cheat sheet free?
Yes. This C# cheat sheet is completely free, with no sign-up required. Bookmark it and come back whenever you need to look up syntax, a collection, or a LINQ method.
What is the difference between value types and reference types in C#?
Value types (
int, double, bool, struct, enum) hold their data directly and are copied when assigned or passed to a method - changing the copy does not affect the original. Reference types (class, string, arrays, List<T>) hold a reference to data on the heap, so two variables can point at the same object and a change through one is visible through the other. string is a reference type but behaves immutably.What is LINQ and when should I use it?
LINQ (Language Integrated Query) is a set of methods like
Where, Select, and OrderBy that let you filter, transform, and aggregate collections with readable, chainable calls instead of manual loops. Use it whenever you would otherwise write a loop to build a filtered or projected list - it is concise and lazily evaluated until you call ToList() or iterate.Can I practice C# online?
Yes. Open the C# playground to run any snippet from this cheat sheet in your browser - no SDK to install. When you want structure, Coddy's free interactive C# course takes you from variables and loops to classes, collections, and LINQ step by step.
Is this cheat sheet good for beginners?
Yes. It is organized from the most common building blocks (types, control flow, methods) down to advanced ones (LINQ, async, generics), so you can use the top sections on day one and grow into the rest.
Related resources
More cheat sheets
