0x50Lesson 6 of 6

Explore LINQ, nullability, and async

Query sequences and understand important modern C# features.

15 min 5-question quiz

By the end of this lesson you can

Use LINQ filters and explain nullable references and async/await.

LINQ provides operators such as Where to filter and Select to transform sequences. Some queries use deferred execution and run when enumerated. Nullable reference types add compile-time analysis for possible null values, but do not automatically check at runtime. async and await compose asynchronous operations without blocking a thread while waiting; async alone does not make CPU-heavy work faster.

Program.cs · C# 12

1using System;
2using System.Linq;
3
4class Program
5{
6    static void Main()
7    {
8        int[] numbers = { 1, 2, 3, 4, 5, 6 };
9        int total = numbers.Where(n => n % 2 == 0).Sum();
10        Console.WriteLine(total);
11    }
12}

Output

The lambda n => n % 2 == 0 is a compact predicate passed to Where. In real applications, async methods commonly return Task or Task<T>; awaiting I/O lets the current thread do other work while the operation is pending.

Key takeaways

LINQ expresses filtering and transformation over sequences.
Nullable analysis warns about possible nulls at compile time.
Async/await helps compose waits without blocking a thread.

Lesson quiz

5 questions · pass with 4 correct · up to 50 XP

Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.

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