Stage 2 of 10 · 6 lessons · ~2 months

C# for real work: LINQ, collections, generics and async

The C# you use every day at work: picking the right collection, querying it with LINQ, writing generic code and making slow I/O async without blocking threads. EF Core and ASP.NET Core build directly on all four.

Start: Collections and when to use each

Lessons· one lesson for each topic, in this order

Start with· follow one of these

CoursePaid
Grokking Data Structures & Algorithms for Coding Interviews
Design Gurus · Beginner · Subscription
Arrays, hash tables, lists, stacks and queues: what every C# collection is built on, with complexity explained
GuideFree
.NET documentation
Microsoft
Free official guides on LINQ, generics, collections and the asynchronous programming model

Practise

Exercism
Keep going on the C# track: the later exercises lean on LINQ, generics and dictionaries
LeetCode
Solve easy array and hash map problems in C# to make collections and LINQ automatic

Keep handy

Learn C#
Return to the official C# modules on collections, LINQ and async when something is unclear

Also worth your time

Asynchronous programming with async and await (opens in a new tab)Read
The official explanation of tasks, await and running work concurrently, with a worked example
Grokking Multithreading and Concurrency for Coding InterviewsGo deeperPaid
Threads, locks, deadlocks and thread safety: what sits underneath async code and the thread pool

Before moving on: Build a console tool that reads a CSV of 10,000 sample transactions asynchronously, reports totals per branch and the top customers with LINQ, flags duplicate references with a HashSet, supports cancellation with Ctrl+C, and has xUnit tests for the report logic.

Tauseef's advice

Write LINQ by hand until grouping and projections feel easy, because EF Core is LINQ with a database behind it. Learn the async rules now as habits: async all the way, pass the token, never block. Fixing them later in a large API is painful.