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What is C#?

• C# is a modern, object-oriented programming language developed by Microsoft as part of the .NET framework. It is widely used for developing Windows applications, web applications, and more.

What is the difference between == and .Equals() in C#?

• The == operator compares the values of two objects for equality, while the .Equals() method checks if two objects are equal based on their contents. The .Equals() method can be overridden in custom classes to provide custom comparison logic.

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What is the difference between String and StringBuilder in C#?

• String is immutable, meaning its value cannot be changed after it's created. StringBuilder, on the other hand, is mutable and allows for efficient manipulation of strings by appending, inserting, or removing characters without creating new objects.

Explain the concept of inheritance in C#.

• Inheritance is a mechanism in which a new class (derived class) is created based on an existing class (base class). The derived class inherits properties, methods, and other members from the base class and can also extend its functionality by adding new members or overriding existing ones.

What is an interface in C#?

• An interface is a reference type that defines a contract for classes to implement. It contains only method signatures, properties, events, or indexers. Classes that implement an interface must provide concrete implementations for all its members.

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What is the difference between IEnumerable and IQueryable in C#?

• IEnumerable represents a collection of objects that can be enumerated using a foreach loop, suitable for in-memory collections. IQueryable represents a query that can be executed against a data source, typically a database, and supports LINQ queries with deferred execution.

What is the purpose of the using statement in C#?

• The using statement is used to ensure that resources like file streams, database connections, etc., are properly disposed of after they are no longer needed. It automatically calls the Dispose() method on objects that implement the IDisposable interface when they go out of scope.

What is a delegate in C#?

• A delegate is a type that represents a reference to a method with a specific signature. It allows methods to be passed as parameters, stored in variables, and invoked dynamically. Delegates are commonly used in event handling and asynchronous programming.

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Explain the difference between ref and out parameters in C#?

• Both ref and out parameters are used to pass arguments by reference instead of by value. However, ref parameters must be initialized before passing them to a method, whereas out parameters do not need to be initialized and are typically used for returning multiple values from a method.

What are the benefits of using LINQ in C#?

• LINQ (Language Integrated Query) provides a unified syntax for querying data from various data sources like collections, arrays, XML, SQL databases, etc. It offers compile-time type checking, intellisense support, and allows for writing more expressive and readable code compared to traditional approaches.

What are the different access modifiers available in C# and explain their visibility scopes?

• C# provides five access modifiers: public, private, protected, internal, and protected internal.
• public: accessible from any code in the same assembly or another assembly.
• private: accessible only within the containing type.
• protected: accessible within the containing type and its derived types.
• internal: accessible within the same assembly.
• protected internal: accessible within the same assembly or from a derived class in another assembly.

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What is the purpose of the virtual and override keywords in C#?

• The virtual keyword is used to declare a method, property, or indexer that can be overridden in derived classes.
• The override keyword is used to provide a new implementation for a virtual member inherited from a base class.

What is the difference between IEnumerable and IQueryable in LINQ?

• IEnumerable represents a sequence of objects that can be enumerated, typically in-memory collections like arrays or lists.
• IQueryable represents a query that can be executed against a data source, such as a database, and supports composition with other LINQ operators.

What is the purpose of the async and await keywords in C#?

• The async keyword is used to declare an asynchronous method, which allows the method to run asynchronously without blocking the calling thread.
• The await keyword is used to pause the execution of an asynchronous method until the awaited task is complete, while allowing the calling thread to continue with other tasks.

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Explain the difference between value types and reference types in C#?

• Value types store their actual values directly in memory, whereas reference types store references (pointers) to the memory location where the values are stored.
• Examples of value types include int, float, and struct. Examples of reference types include class, interface, and string.

What is boxing and unboxing in C#?

• Boxing is the process of converting a value type to a reference type, which involves wrapping the value inside an object.
• Unboxing is the process of extracting the value from a boxed object and converting it back to its original value type.

What is the purpose of the using directive in C#?

• The using directive is used to import namespaces, allowing types defined in those namespaces to be used in the current code file without fully qualifying their names.

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Explain the difference between Array and ArrayList in C#?

• 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.

What is an anonymous type in C#?

• An anonymous type is a type without a name that is automatically generated by the compiler to encapsulate a set of properties or fields. They are often used in LINQ queries to represent projected data.

What is the purpose of the params keyword in C#?

• The params keyword allows a method to accept a variable number of parameters of the same type, making it more flexible when calling the method with multiple arguments.

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What is the try, catch, finally block used for in C#?

• The try block is used to enclose code that might throw exceptions. The catch block is used to handle specific types of exceptions that are thrown within the try block. The finally block is used to specify code that should always be executed, regardless of whether an exception occurs or not.

What are the different types of exceptions in C#?

• C# exceptions can be divided into two main categories: system exceptions (derived from System.Exception) and application exceptions (derived from ApplicationException). System exceptions include NullReferenceException, ArgumentException, InvalidOperationException, etc.

Explain the concept of polymorphism in C# with an example.

• Polymorphism allows objects of different types to be treated as objects of a common base type. This can be achieved through inheritance and method overriding. For example, a Circle class and a Rectangle class can both inherit from a common Shape class and override a Draw method to provide different implementations.

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What is the difference between List<T> and Dictionary<TKey, TValue> in C#?

• List<T> represents a dynamic collection of elements of a specified type, typically accessed by index. Dictionary<TKey, TValue> represents a collection of key-value pairs, where each key is unique and used to access its associated value.

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