.NET interviews move between C# the language and the runtime underneath it — the CLR, the GC, how async/await actually works — before landing on ASP.NET Core and Entity Framework Core, where most real-world questions live. Below are the questions asked most often, each with a model answer. Junior: core theory, definitions, and simple practical cases.
A value type (struct, int, bool, enum) holds its data directly and is copied on assignment; a reference type (class, string, arrays) holds a pointer to the heap, and assignment copies the pointer, not the data. Passing a struct to a method and mutating it inside only changes the copy unless you pass it by ref.
Boxing wraps a value type in a heap object so it can be used as object — for example passing an int into a non-generic collection like ArrayList. Unboxing casts it back to the value type. Each box is a heap allocation, which is why generic collections like List<int> are preferred — they never box.
They let the compiler distinguish string ("never null") from string? ("can be null") and warn you when you dereference a nullable value without checking it first. It is a compile-time hint, not a runtime guarantee, but it catches a large share of NullReferenceException bugs before the code ever runs.
finally always runs, whether an exception was thrown or not, so it is where you put cleanup code manually. using is shorthand for a try/finally that calls Dispose() on an IDisposable object — a file handle, a database connection — guaranteeing it is released even if the code inside throws.
Where filters a sequence by a predicate, Select projects each element into a new shape, and OrderBy sorts it. They can be chained — list.Where(x => x.Active).Select(x => x.Name).OrderBy(n => n) — and none of them run until the result is enumerated, which is the deferred-execution behavior LINQ is built on.
Instead of a class creating its own dependencies with new, they are provided from the outside — usually through the constructor — which makes the class testable and swappable. ASP.NET Core ships a built-in container: services are registered in Program.cs with AddScoped, AddTransient or AddSingleton, and the framework resolves and injects them wherever they are requested.
In a real interview you speak under pressure. Cam asks these same questions, scores every answer, and shows exactly what to fix.
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