C# Interview Questions (2026) — 15 Real Questions + AI Mock Interview
C# interviews test how well you understand the .NET runtime beneath the syntax: value vs reference types, memory, async, and LINQ. Loops for backend, enterprise, game (Unity), and cloud roles open with core-language and OOP questions, move into LINQ and async, and finish with a coding round. In 2026 async/await fluency and modern C# features are expected. Below are the questions asked most, with what a senior interviewer is listening for.
15 C# interview questions you'll actually get asked
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1. Value types vs reference types.
How a senior interviewer scores this: Stack/inline vs heap + reference; predicts copy-vs-share behaviour on assignment.
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2. What are boxing and unboxing, and why care?
How a senior interviewer scores this: Value type wrapped on the heap; flags the allocation/perf cost in hot paths.
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3. How does memory management and the GC work in .NET?
How a senior interviewer scores this: Generational GC, IDisposable/using for unmanaged resources, and the finalizer cost.
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4. Explain async/await and Task.
How a senior interviewer scores this: Frees the thread on IO waits; avoids async void and .Result deadlocks; uses ConfigureAwait where relevant.
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5. IEnumerable vs IQueryable.
How a senior interviewer scores this: In-memory iteration vs translated-to-source queries; knows deferred execution and where filtering happens.
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6. Abstract class vs interface in C#.
How a senior interviewer scores this: Shared implementation/state vs contract; aware of default interface methods in modern C#.
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7. ref vs out vs in parameters.
How a senior interviewer scores this: ref in/out, out must be assigned, in is read-only by reference; uses them sparingly.
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8. What are delegates, events, Func and Action?
How a senior interviewer scores this: Type-safe function pointers; events as the publish/subscribe wrapper over delegates.
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9. Walk through a LINQ query and its execution.
How a senior interviewer scores this: Composes methods, understands deferred execution, and knows when it hits the database.
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10. var vs dynamic.
How a senior interviewer scores this: var is compile-time inferred; dynamic defers to runtime and loses type safety.
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11. struct vs class — when a struct?
How a senior interviewer scores this: Small, immutable, value-semantic data; aware of copy cost and boxing risks.
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12. Why is string immutable, and when use StringBuilder?
How a senior interviewer scores this: Immutability + interning; StringBuilder for repeated concatenation to avoid allocations.
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13. How do nullable reference types help?
How a senior interviewer scores this: Compiler-tracked nullability catches NREs at build time; reads the warnings instead of suppressing.
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14. Properties vs fields.
How a senior interviewer scores this: Encapsulation, validation, and binding; uses auto-properties and knows backing fields.
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15. How do you handle exceptions well in C#?
How a senior interviewer scores this: Catches specific types, avoids swallowing, uses finally/using; knows when a custom exception is justified.
How C# answers are scored
Strong candidates aren't just correct — they're graded on five dimensions a real interviewer weighs: technical correctness, communication, problem-solving, depth, and culture fit. For C# specifically, the fastest score jump is narrating your reasoning and trade-offs out loud before you write code. Each question above lists what the interviewer is actually listening for.
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C# interview FAQ
What level are these C# interview questions for?
Junior through senior backend, enterprise, Unity, and cloud roles. Screens cover OOP and value vs reference types; senior loops add async, LINQ internals, and memory. Async/await fluency is a common dividing line.
How should I prepare for a C# interview in 2026?
Get fluent in async/await — interviewers probe deadlocks, async void, and Task behaviour. Practise LINQ and deferred execution out loud, and be ready to reason about value vs reference semantics in a coding round.
Do C# interviews cover .NET internals?
Often, for mid and senior roles. Expect questions on the GC, value vs reference types, boxing, and IDisposable. Understanding what the runtime does — not just the syntax — is what moves you up a band.