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📝 Basics
Variables and types basics
int age = 30;
double price = 9.99;
string name = "Alice";
bool active = true;
var items = new List<string>(); // type inferred
// Constants
const int MaxRetries = 3;
// Nullable types
int? maybeNull = null;
string? maybeName = null;String interpolation and formatting basics
string name = "World";
Console.WriteLine($"Hello, {name}!");
Console.WriteLine($"Price: {9.99:C}"); // $9.99
Console.WriteLine($"Date: {DateTime.Now:d}"); // 3/15/2026
// Raw string literals (C# 11)
string json = """
{
"name": "Alice",
"age": 30
}
""";Control flow basics
// Pattern matching switch
string result = status switch
{
"active" => "Running",
"paused" => "On hold",
_ => "Unknown"
};
// If / else
if (age >= 18) { /* ... */ }
else if (age >= 13) { /* ... */ }
else { /* ... */ }
// Ternary
string label = age >= 18 ? "adult" : "minor";📦 Collections
List, Dictionary, HashSet collections
// List
var names = new List<string> { "Alice", "Bob" };
names.Add("Charlie");
names.Remove("Bob");
bool has = names.Contains("Alice");
// Dictionary
var ages = new Dictionary<string, int>
{
["Alice"] = 30,
["Bob"] = 25
};
ages["Charlie"] = 35;
ages.TryGetValue("Alice", out int age);
// HashSet
var tags = new HashSet<string> { "a", "b" };
tags.Add("c");
tags.UnionWith(new[] { "d", "e" });Arrays and spans collections
int[] nums = { 1, 2, 3, 4, 5 };
int[] slice = nums[1..3]; // { 2, 3 }
int last = nums[^1]; // 5
// Span (stack-allocated view, no copy)
Span<int> span = nums.AsSpan(1, 3);🔍 LINQ
Filtering, mapping, aggregating linq
var numbers = new[] { 1, 2, 3, 4, 5, 6 };
var evens = numbers.Where(n => n % 2 == 0);
var doubled = numbers.Select(n => n * 2);
var sum = numbers.Sum();
var first = numbers.First(n => n > 3); // 4
var any = numbers.Any(n => n > 10); // false
// Chaining
var result = numbers
.Where(n => n > 2)
.Select(n => n * 10)
.OrderByDescending(n => n)
.ToList();GroupBy, Join, Distinct linq
var people = new[]
{
new { Name = "Alice", Dept = "Eng" },
new { Name = "Bob", Dept = "Eng" },
new { Name = "Charlie", Dept = "Sales" },
};
// Group
var groups = people.GroupBy(p => p.Dept);
foreach (var g in groups)
Console.WriteLine($"{g.Key}: {g.Count()}");
// Distinct
var unique = names.Distinct().ToList();
// ToDictionary
var dict = people.ToDictionary(p => p.Name, p => p.Dept);⚡ Async / Await
Async methods and Task async
async Task<string> FetchDataAsync(string url)
{
using var client = new HttpClient();
return await client.GetStringAsync(url);
}
// Parallel async
var tasks = urls.Select(url => FetchDataAsync(url));
string[] results = await Task.WhenAll(tasks);
// Async streams
async IAsyncEnumerable<int> GenerateAsync()
{
for (int i = 0; i < 10; i++)
{
await Task.Delay(100);
yield return i;
}
}🏗️ OOP and Records
Classes, interfaces, records oop
// Record (immutable data class)
public record User(string Name, string Email);
var user = new User("Alice", "alice@example.com");
var updated = user with { Email = "new@example.com" };
// Interface
public interface IRepository<T>
{
Task<T?> GetByIdAsync(int id);
Task<IEnumerable<T>> GetAllAsync();
}
// Class with primary constructor (C# 12)
public class UserService(IRepository<User> repo)
{
public Task<User?> GetUser(int id) => repo.GetByIdAsync(id);
}Pattern matching oop
string Describe(object obj) => obj switch
{
int n when n > 0 => "positive int",
string { Length: > 10 } => "long string",
null => "null",
_ => "something else"
};
// List patterns (C# 11)
int[] arr = { 1, 2, 3 };
if (arr is [1, _, 3])
Console.WriteLine("Starts with 1, ends with 3");🛠️ Common Patterns
Dependency injection (ASP.NET) aspnet
// Program.cs
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped<IUserService, UserService>();
builder.Services.AddDbContext<AppDbContext>();
var app = builder.Build();
app.MapGet("/users", async (IUserService svc) =>
await svc.GetAllAsync());
app.Run();Minimal API endpoints aspnet
app.MapGet("/items", () => db.Items.ToListAsync());
app.MapGet("/items/{id}", async (int id) =>
await db.Items.FindAsync(id) is Item item
? Results.Ok(item)
: Results.NotFound());
app.MapPost("/items", async (Item item) =>
{
db.Items.Add(item);
await db.SaveChangesAsync();
return Results.Created($"/items/{item.Id}", item);
});Null handling basics
// Null-conditional
int? length = name?.Length;
// Null-coalescing
string display = name ?? "Unknown";
// Null-coalescing assignment
name ??= "Default";
// Null-forgiving (suppress warning)
string definitelyNotNull = maybeNull!;Quick access: Raycast lets you search commands, snippets, and cheat sheets instantly from your keyboard. Free for Mac.
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