C# Interview Prep: 100 Common Questions for 0-3 Years Experience

Common C# Interview Questions 

Basics of C# Language:

1. What is C#? C# (pronounced C sharp) is a modern, object-oriented programming language developed by Microsoft. It is widely used for building Windows applications, web applications, and various types of software.

1. Differentiate between value types and reference types. Value types store the actual data, whereas reference types store references to the memory locations where the data is held. Examples of value types include integers and floating-point numbers, while examples of reference types include classes and interfaces.

1. Explain the difference between == and Equals() in C#. == is used for comparing the values of two variables, while Equals() is a method used for comparing the contents of objects. Equals() can be overridden for custom comparison logic.

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3. What is the purpose of the using statement in C#? The using statement is used for automatic resource management, ensuring that the resources are properly disposed of when they are no longer needed, such as closing files or releasing

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6. Describe the difference between const and readonly in C#. const is a compile-time constant, and its value cannot be changed after compilation. readonly allows a value to be assigned at runtime or in the constructor, and it cannot be changed afterward.

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8. What is the significance of the var keyword? The var keyword is used for implicit typing. The type of the variable is determined by the compiler based on the assigned value, reducing the need for explicit type declarations.

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10. Explain the purpose of this keyword in C#. this refers to the current instance of a class and is used to qualify members to avoid naming conflicts between class fields and parameters with the same name.

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12. Differentiate between string and StringBuilder in C#. string is immutable, meaning its value cannot be changed after creation. StringBuilder is mutable and is more efficient when performing concatenation operations on strings.

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14. What are nullable types in C#? Nullable types allow variables to have a value of null in addition to their normal range. They are defined using the nullable type modifier '?'.

Object-Oriented Programming (OOP):

10. 10. Define encapsulation in C#. Encapsulation is the bundling of data and methods that operate on the data into a single unit (class). It helps in controlling access to the internal state of an object.

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    12. Explain inheritance and its types in C#. Inheritance is a mechanism where a new class can inherit properties and behaviors from an existing class. Types of inheritance in C# include single inheritance, multiple inheritance through interfaces, and hierarchical inheritance.

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    14. Describe polymorphism and its types. Polymorphism allows objects to be treated as instances of their base class, enabling code reuse and flexibility. Types of polymorphism include compile-time (method overloading) and runtime (method overriding) polymorphism.

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    16. What is the difference between abstract classes and interfaces? Abstract classes can have both abstract and concrete methods, and they can have fields. Interfaces only define method signatures and constants, and a class can implement multiple interfaces but inherit from only one abstract class.

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    18. How does C# support multiple inheritance? C# supports multiple inheritance through interfaces. A class can implement multiple interfaces, enabling it to inherit behaviors from multiple sources.

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    20. Discuss the importance of the sealed keyword in C#. The sealed keyword is used to prevent a class from being inherited by other classes. It is often applied to classes that are not intended to be extended.

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    22. What is method hiding in C#? Method hiding occurs when a derived class provides a new implementation for a method already defined in its base class. It is achieved by using the new keyword.

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    24. Explain the concept of constructor chaining. Constructor chaining involves calling one constructor from another within the same class. It helps avoid code duplication and ensures that common initialization logic is executed.

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    26. Describe the use of the base keyword in C#. The base keyword is used to access members of the base class within the derived class. It is often used to call the constructor of the base class or to qualify a member that is hidden by a member in the derived class.

    27. C# Programming Concepts:

        19. What is the purpose of the try, catch, and finally blocks in exception handling? The try block contains the code that might throw an exception, the catch block handles the exception if one occurs, and the finally block contains code that will always be executed, regardless of whether an exception occurs.

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        21. Discuss the role of the static keyword in C#. The static keyword is used to define static members that belong to the type itself rather than an instance of the type. Static members are shared among all instances of the class.

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        23. Explain the significance of the params keyword in method parameters. The params keyword allows a method to accept a variable number of parameters of a specified type. It simplifies method calls by allowing the caller to provide a variable number of arguments.

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        25. How do you handle exceptions in C#? Exceptions in C# are handled using try-catch blocks. The try block contains the code that might throw an exception, and the catch block handles the exception by specifying the type of exception to catch.

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        27. Discuss the differences between Array and ArrayList. Array is a fixed-size collection of elements of the same type, while ArrayList is a dynamic collection that can grow or shrink in size and can hold elements of different types.

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        29. What is the role of the delegate keyword in C#? A delegate in C# is a type-safe function pointer that holds references to methods. It is often used to implement event handling and callback mechanisms.

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        31. Describe events and their usage in C#. Events in C# allow one class to notify other classes or objects when certain actions occur. They are commonly used for implementing the observer pattern and event-driven programming.

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        33. Explain the concept of lambda expressions. Lambda expressions are concise, anonymous functions in C#. They simplify the syntax for defining methods, especially when working with delegates or functional interfaces.

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        35. Discuss the use of LINQ in C#. LINQ (Language Integrated Query) is a set of language features that allow querying data from different data sources in a type-safe manner. It includes query operators for filtering, sorting, and projecting data.

        19. Memory Management:

        20. 28. What is garbage collection in C#? Garbage collection is the automatic process of reclaiming memory occupied by objects that are no longer in use. The .NET runtime's garbage collector manages memory automatically.

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            30. Discuss the differences between Dispose() and Finalize() methods. The Dispose() method is used for releasing unmanaged resources, and it should be called explicitly. The Finalize() method is part of the garbage collection process and is called automatically before an object is reclaimed by the garbage collector.

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            32. Explain the purpose of the using statement in the context of IDisposable. The using statement is a syntactic sugar for working with objects that implement the IDisposable interface. It ensures that the Dispose() method is called when the object goes out of scope.

            C# Programming Patterns:

            31. 31. Describe the Singleton pattern in C#. The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. It involves a private constructor, a private static instance, and a public static method for obtaining the instance.

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                33. Discuss the Observer pattern and how it can be implemented in C#. The Observer pattern defines a one-to-many dependency between objects, where one object (the subject) notifies its observers of any state changes. In C#, this can be implemented using events and delegates.

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