Questions
C# questions
Choose a question page, learn the concept, then test your understanding with a quiz.
Using Directives Inside vs Outside a Namespace in C#
Learn why C# using directives can be placed inside or outside a namespace, how scope changes, and what StyleCop is enforcing.
What Is a NullReferenceException in C# and How Do You Fix It?
Learn what a NullReferenceException means in C#, why it happens, and practical ways to prevent and fix null reference errors.
What the ?? Operator Means in C#
Learn what the ?? null-coalescing operator means in C#, how it works, when to use it, and how it differs from the ternary operator.
What the [Flags] Enum Attribute Means in C#
Learn what the [Flags] enum attribute does in C#, how bit flags work, and how to combine enum values safely with clear examples.
What the yield Keyword Does in C#: Iterators and Lazy Enumeration
Learn what the C# yield keyword does, how yield return works, and why it is used to build lazy iterators and enumerable sequences.
When to Use struct vs class in C#: Value Types Explained
Learn when to use struct instead of class in C#, including value semantics, size guidelines, immutability, and practical examples.
Why Calling a Virtual Member in a Constructor Is Risky in C#
Learn why calling a virtual member inside a constructor is risky in C#, what can go wrong, and safer alternatives to use instead.
Why Dictionary Is Preferred Over Hashtable in C#
Learn why Dictionary<TKey, TValue> is usually preferred over Hashtable in C#, including type safety, performance, syntax, and real usage.
Why Inheriting from List<T> Is Usually a Bad Idea in C#
Learn when to inherit from List<T> in C#, why composition is usually better, and how to model custom collections safely.
Why Override GetHashCode When Overriding Equals in C#
Learn why GetHashCode must match Equals in C#, how hash-based collections work, and how to implement both methods correctly.
Why \d Can Be Slower Than [0-9] in C# Regex
Learn why \d may be slower than [0-9] in C# regex, how digit classes work, and when to use \d, [0-9], or explicit character sets.
decimal vs double in C#: When to Use Each Type
Learn the difference between decimal and double in C#, when to use each, and which type is best for money and precision-sensitive calculations.
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