C# Cheatsheet - C# Syntax & .NET Reference

This reference is for .NET developers building web APIs, services, or desktop apps, focusing on the C# syntax you write every day: classes and interfaces with their access modifiers, LINQ for querying collections instead of hand-written loops, async/await for I/O-bound work, generics and delegates, and the property/event model. Unlike a flat C# feature list, entries are grouped by the language construct and note where C# behavior differs from Java or JS. After reading you should be able to replace a nested loop with a composed LINQ query, set up an async method without deadlocking, and design a type with properties, events and a delegate.

Languages·39 commands·Last updated 2026-07-21

Classes & Interfaces 7

public class MyClass { }

Class definition

public interface IMyInterface { void Method(); }

Interface definition

public class Derived : Base, IMyInterface { }

Inherit and implement an interface

public abstract class AbstractClass { }

Abstract class

public sealed class SealedClass { }

Sealed class (not inheritable)

public static class Utils { }

Static class

public record Person(string Name, int Age);

Record type (C# 9)

Properties & Methods 6

public int Age { get; set; }

Auto-property

public string Name { get; init; }

Init-only property (C# 9)

public int Age => _age;

Read-only property (expression-bodied)

public void Method() { }

Method definition

public int Add(int a, int b) => a + b;

Expression-bodied method

public event EventHandler MyEvent;

Event definition

LINQ Queries 8

var result = list.Where(x => x > 5);

Filter

var result = list.Select(x => x * 2);

Map

var result = list.OrderBy(x => x.Age);

Sort

var result = list.GroupBy(x => x.Category);

Group

var result = list.First(x => x.Id == 1);

First match

var result = list.Any(x => x > 0);

Any exists

var result = list.Sum(x => x.Price);

Sum

var result = list.Aggregate((a, b) => a + b);

Aggregate

Asynchronous 6

public async Task<int> GetDataAsync() { }

Async method

await Task.Delay(1000);

Async delay

var result = await httpClient.GetStringAsync(url);

Async HTTP request

Task.Run(() => { });

Run on a background thread

await Task.WhenAll(task1, task2);

Await multiple tasks in parallel

CancellationTokenSource cts = new();

Cancellation token

Generics & Delegates 6

public class Stack<T> { }

Generic class

public T Max<T>(T a, T b) where T : IComparable<T> { }

Generic constraint

public delegate void MyDelegate(string msg);

Delegate definition

public event Action<string> OnMessage;

Action delegate

public Func<int, int, int> add = (a, b) => a + b;

Func delegate

public Predicate<int> isPositive = x => x > 0;

Predicate delegate

Collections & Dictionaries 6

List<int> list = new() { 1, 2, 3 };

List

Dictionary<string, int> dict = new();

Dictionary

HashSet<int> set = new() { 1, 2, 3 };

Hash set

Queue<int> queue = new();

Queue

Stack<int> stack = new();

Stack

var tuple = (1, "hello");

Tuple

Tips

LINQ queries are lazily evaluated; they run only when the results are enumerated.
async/await is core to asynchronous programming; avoid blocking the UI thread.
C# 9 introduced record types, ideal for immutable data models.

Official References

Each command links to its official documentation below, so you can verify the latest usage and read deeper.

Official Docs

Maintained by LaoHand

Publicly updated on Jul 21, 2026, continuously proofread against official docs.

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