Top 25 C# (Unknown but I’ll tell you) Interview Questions and In-Depth Answers (2023)
Navigating a C# interview can be challenging, especially when facing unexpected or lesser-known questions.
Let’s delve into 25 such questions that might catch you off guard, along with detailed answers.
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1. What is the DLR (Dynamic Language Runtime) in C#?
Answer: The DLR is a runtime environment introduced in .NET Framework 4.0, facilitating the dynamic execution of languages like Python and Ruby in addition to C#. It enables late binding, dynamic method invocation, and dynamic code generation.
2. Explain the concept of Tuple in C#.
Answer: A Tuple is a data structure introduced in C# 4.0 that allows grouping multiple elements of different types into a single, lightweight object. Tuples are immutable and often used when a method needs to return multiple values.
3. What is the StackFrame class in C#?
Answer: StackFrame is part of the System.Diagnostics namespace, representing a function call on the call stack. It provides information about the method, file, and line number in the code where the frame is located, aiding in debugging.
4. Explain the concept of Covariant Returns.
Answer: Covariant Returns, introduced in C# 9.0, allow a derived class to override a base class method with a return type that is more specific than the return type of the base class method. This simplifies code and enhances type safety.
5. What is the in modifier in C# 7.2 onwards?
Answer: The in modifier is used in method parameters to indicate that the parameter is read-only. It is particularly useful for performance optimization in scenarios where the value does not need to be modified within the method.
6. Explain the ValueTask class in C#.
Answer: ValueTask is a part of the System.Threading.Tasks namespace introduced in C# 7.0. It represents a task-like object that can be used to perform asynchronous operations more efficiently than Task in certain scenarios, reducing allocations.
7. What is the purpose of the Span<T> type in C#?
Answer: Span<T> is a type introduced in C# 7.2 to represent a contiguous region of arbitrary memory. It is particularly useful for low-level operations and can improve performance by avoiding unnecessary memory allocations.
8. Explain the concept of IAsyncEnumerable and await foreach.
Answer: IAsyncEnumerable is an interface introduced in C# 8.0 for asynchronous streaming of data. await foreach is a language feature that simplifies asynchronous iteration over an IAsyncEnumerable, making asynchronous code more readable.
9. What is the difference between Task.Run and Task.Factory.StartNew?
Answer: While both methods start a new task, Task.Run is preferred for CPU-bound operations, and Task.Factory.StartNew is more suitable for I/O-bound operations. Task.Run uses TaskScheduler.Default, which is optimized for CPU-bound tasks.
10. Explain the concept of Caller Information attributes.
Answer: Caller Information attributes, introduced in C# 5.0, allow a method to obtain information about the caller’s file path, line number, and member name. This is achieved using attributes like CallerFilePath, CallerLineNumber, and CallerMemberName.
11. What is the Obsolete attribute, and how is it used?
Answer: The Obsolete attribute marks elements (methods, classes, etc.) as obsolete or deprecated, indicating that they should no longer be used. It helps in providing a clear migration path for developers and avoiding the use of outdated features.
12. Explain the concept of Code Contracts in C#.
Answer: Code Contracts are a set of tools introduced in .NET Framework 4.0 that allow developers to express coding assumptions in the form of preconditions, postconditions, and object invariants. These contracts can be checked at runtime and provide better code documentation and verification.
13. What are expression-bodied members in C#?
Answer: Expression-bodied members, introduced in C# 6.0, allow concise syntax for writing one-liner methods, properties, and other members. For example, a property getter can be expressed as int Square => Value * Value;, providing a cleaner and more readable code.
14. Explain the concept of Interpolated Strings.
Answer: Interpolated Strings, introduced in C# 6.0, allow embedding expressions within string literals using the $ prefix. This enables more readable and concise string formatting without using concatenation or placeholders.
15. What is the Span<T>.Slice method used for?
Answer: The Slice method in Span<T> is used to create a new Span<T> that represents a subrange of the original Span<T>. It allows efficient manipulation of portions of arrays or memory regions without creating additional copies.
16. Explain the concept of Pattern Matching in C#.
Answer: Pattern Matching, introduced in C# 7.0, allows developers to write more expressive and concise code for conditional statements, type checks, and switch statements. It simplifies complex conditional logic and enhances code readability.
17. What is the Record type introduced in C# 9.0?
Answer: Records are a new reference type introduced in C# 9.0, designed for immutable data modeling. They simplify the creation of classes primarily used for holding data by providing built-in features like value-based equality, deconstruction, and immutability.
18. Explain the concept of stackalloc in C#.
Answer: The stackalloc keyword in C# is used to allocate memory on the stack rather than the heap. It is often used in performance-critical scenarios, such as working with arrays in a stack-allocated memory block.
19. What is the use of the Obsolete attribute with error and warning messages?
Answer: The Obsolete attribute allows developers to provide error or warning messages, guiding users on the reasons for deprecation and suggesting alternative approaches. This ensures a smoother transition when updating code.
20. Explain the CallerLineNumber attribute.
Answer: The CallerLineNumber attribute, used in conjunction with optional parameters, automatically populates the line number from which a method is called. This helps in logging and debugging by providing context about the calling code location.
21. What is the DefaultLiteral feature in C# 7.1?
Answer: The DefaultLiteral feature allows the use of default as a value for any type, even if it's not a reference type. This simplifies code and aligns with the common use of default for nullable value types.
22. Explain the concept of Nullable Reference Types.
Answer: Introduced in C# 8.0, Nullable Reference Types help catch null-related errors during compile-time. It adds a level of safety by distinguishing between types that can be nullable and those that cannot, reducing the likelihood of null reference exceptions.
23. What is With expression in C# 9.0 used for?
Answer: The With expression is used in records (introduced in C# 9.0) to create a new instance of a record with modified values. It simplifies the process of updating records while maintaining immutability.
24. Explain the concept of Source Generators.
Answer: Source Generators, introduced in C# 9.0, allow the generation of additional source code during compilation. They enable developers to extend the compiler and automate repetitive tasks, resulting in more efficient code generation.
25. What is covariant and contravariant generic types in C#?
Answer: Covariant and contravariant refer to the compatibility of generic types when dealing with inheritance. Covariant types allow using a more derived type, while contravariant types allow using a less derived type. This concept is crucial in maintaining flexibility when working with generic collections and interfaces.
Conclusion
Mastering these lesser-known aspects of C# will not only impress interviewers but also enhance your overall proficiency in the language.
Keep exploring and stay prepared for any curveball questions that might come your way during C# interviews.
Happy Job hunting!
