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<\/a><\/p>Practice C# Interview Questions and Answers<\/h2>
Below are the top 50 C# interview questions for freshers with answers:<\/p>
1. How do you declare and initialize a variable in C#?<\/h3>
Answer:<\/strong><\/p> Declare a variable by specifying its type and name, followed by initialization with a value using the assignment operator.<\/p> int number = 5;<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> == compares the reference or value type of objects, while Equals()<\/strong> compares the actual content of the objects.<\/p> string a = “hello”; Answer:<\/strong><\/p> Use the const<\/strong> keyword to declare a constant, which means its value cannot be changed after initialization.<\/p> const double Pi = 3.14159;<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> The using<\/strong> statement is used to include namespaces and ensure that resources are disposed of correctly at the end of their usage.<\/p> using System.IO;<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Define an enum<\/strong> using the enum keyword, followed by the enum name and a list of named constants.<\/p> enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Define a class using the class<\/strong> keyword and instantiate it using the new keyword.<\/p> class Car { Answer:<\/strong><\/p> A class is a blueprint or template for objects, while an object is an instance of a class, containing data and methods defined in the class.<\/p> Car myCar = new Car(); \/\/ `myCar` is an object, `Car` is the class<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Encapsulation is implemented using access modifiers like private<\/strong>, protected<\/strong>, and public<\/strong> to restrict access to class members.<\/p> class Account { Answer:<\/strong><\/p> Inheritance allows a class to inherit members from another class using the :<\/strong> symbol. The derived class inherits properties and methods from the base class.<\/p> class Vehicle { Answer:<\/strong><\/p> Polymorphism allows methods to have different implementations in derived classes. It is achieved using method overriding with the virtual<\/strong> and override<\/strong> keywords.<\/p> class Animal { Answer:<\/strong><\/p> An interface is implemented by a class using the :<\/strong> symbol. The class must provide implementations for all interface members.<\/p> interface IDriveable { Answer:<\/strong><\/p> An abstract class can have method implementations and fields, while an interface can only have method declarations. A class can inherit multiple interfaces but only one abstract class.<\/p> abstract class Animal { Answer:<\/strong><\/p> Use try<\/strong>, catch<\/strong>, and finally<\/strong> blocks to handle exceptions, allowing you to manage runtime errors gracefully.<\/p> try { Answer:<\/strong><\/p> A delegate is a type-safe function pointer. It is declared using the delegate<\/strong> keyword and can point to methods with a matching signature.<\/p> public delegate void PrintMessage(string message); Answer:<\/strong><\/p> A generic class is defined using a type parameter that allows the class to operate on different data types.<\/p> class GenericClass<T> { Answer:<\/strong><\/p> LINQ allows you to query collections using query syntax or method syntax, enabling powerful filtering, sorting, and aggregation operations.<\/p> int[] numbers = { 5, 3, 9, 1 }; Answer:<\/strong><\/p> List<T><\/strong> is a generic collection that provides dynamic array-like storage for elements. Use the Add<\/strong> method to add elements.<\/p> List<int> numbers = new List<int>(); Answer:<\/strong><\/p> Use the Max()<\/strong> method provided by LINQ to find the maximum value in a list or collection.<\/p> List<int> numbers = new List<int> { 1, 5, 3 }; Answer:<\/strong><\/p> IEnumerable<\/strong> is used for in-memory collections, while IQueryable<\/strong> is designed for querying data from out-of-memory sources like databases, allowing for deferred execution and remote querying.<\/p> IEnumerable<int> numbers = new List<int> { 1, 2, 3 };<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Use the group by<\/strong> clause in LINQ to group elements in a collection based on a specific key.<\/p> var grouped = from n in numbers Answer:<\/strong><\/p> Use the StreamReader<\/strong> class in a using<\/strong> block to read the contents of a file line by line.<\/p> using (StreamReader sr = new StreamReader(“file.txt”)) { Answer:<\/strong><\/p> Use the StreamWriter<\/strong> class to write text to a file, which creates a new file or appends to an existing one.<\/p> using (StreamWriter sw = new StreamWriter(“file.txt”)) { Answer:<\/strong><\/p> Use the File.Exists()<\/strong> method to check whether a specific file exists in the specified path.<\/p> bool exists = File.Exists(“file.txt”);<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Use the File.Copy()<\/strong> method to copy a file from one directory to another, specifying the source and destination paths.<\/p> File.Copy(“source.txt”, “destination.txt”);<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Use the File.Delete()<\/strong> method to delete a file from the filesystem by providing its path.<\/p> File.Delete(“file.txt”);<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> An event is a message that objects send to signal the occurrence of an action. Declare an event<\/strong> using the event keyword and a delegate type.<\/p> public event EventHandler MyEvent;<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Subscribe to an event by attaching an event handler method using the +=<\/strong> operator.<\/p> MyEvent += new EventHandler(EventHandlerMethod);<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> A multicast delegate can reference multiple methods. When invoked, all methods in the delegate chain are called in sequence.<\/p> public delegate void Notify(); Answer:<\/strong><\/p> Use the -=<\/strong> operator to remove a method from a delegate’s invocation list.<\/p> del -= Method1;<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Raise an event by invoking it, typically using a protected virtual method to ensure it’s properly raised by derived classes.<\/p> protected virtual void OnMyEvent() { Answer:<\/strong><\/p> Create a custom exception by deriving a class from Exception<\/strong> and implementing appropriate constructors.<\/p> public class MyCustomException : Exception { Answer:<\/strong><\/p> throw<\/strong> preserves the original stack trace, while throw ex<\/strong> resets the stack trace, making it harder to trace the original source of the exception.<\/p> try { Answer:<\/strong><\/p> Use a try-finally<\/strong> block to execute code that must run whether or not an exception is thrown, such as resource cleanup.<\/p> try { Answer:<\/strong><\/p> The StackTrace<\/strong> class provides information about the current call stack, useful for debugging and logging.<\/p> StackTrace st = new StackTrace(); Answer:<\/strong><\/p> Log exceptions by writing them to a file, database, or logging framework like log4net<\/strong> or NLog<\/strong>, typically inside a catch<\/strong> block.<\/p> try { Answer:<\/strong><\/p> Create a new thread using the Thread<\/strong> class, passing a ThreadStart<\/strong> delegate or lambda expression as the method to run.<\/p> Thread myThread = new Thread(new ThreadStart(MyMethod)); Answer:<\/strong><\/p> The Task<\/strong> class represents an asynchronous operation. Use Task.Run()<\/strong> to execute a method asynchronously.<\/p> Task.Run(() => { Answer:<\/strong><\/p> Mark a method with async<\/strong> and use await<\/strong> to asynchronously wait for the completion of a task.<\/p> public async Task<int> GetDataAsync() { Answer:<\/strong><\/p> A ThreadPool<\/strong> manages a pool of worker threads, reducing the overhead of thread creation. Use ThreadPool.QueueUserWorkItem()<\/strong> to queue tasks.<\/p> ThreadPool.QueueUserWorkItem(state => { Answer:<\/strong><\/p> Use the CancellationTokenSource<\/strong> and CancellationToken<\/strong> to signal and check for cancellation in a task.<\/p> CancellationTokenSource cts = new CancellationTokenSource(); Answer:<\/strong><\/p> Define a C# class with properties corresponding to the database table columns, and annotate it with data annotations if needed.<\/p> public class Product { Answer:<\/strong><\/p> Use the DbContext<\/strong> to perform Create, Read, Update, and Delete operations on the database.<\/p>2. What is the difference between == and Equals() in C#?<\/h3>
\nstring b = “hello”;
\nbool result = a == b; \/\/ True
\nbool result2 = a.Equals(b); \/\/ True<\/p>\n<\/div><\/div>3. How do you create a constant in C#?<\/h3>
4. What is the purpose of the using statement in C#?<\/h3>
5. How do you define an enum in C#?<\/h3>
6. How do you create a class in C# and instantiate an object of that class?<\/h3>
\npublic string Make { get; set; }
\n}
\nCar myCar = new Car();<\/p>\n<\/div><\/div>7. What is the difference between a class and an object in C#?<\/h3>
8. How do you implement encapsulation in C#?<\/h3>
\nprivate decimal balance;
\npublic void Deposit(decimal amount) {
\nbalance += amount;
\n}
\n}<\/p>\n<\/div><\/div>9. What is inheritance, and how do you implement it in C#?<\/h3>
\npublic string Brand { get; set; }
\n}
\nclass Car : Vehicle {
\npublic int Wheels { get; set; }
\n}<\/p>\n<\/div><\/div>10. What is polymorphism in C#, and how do you achieve it?<\/h3>
\npublic virtual void Speak() {
\nConsole.WriteLine(“Animal speaks”);
\n}
\n}
\nclass Dog : Animal {
\npublic override void Speak() {
\nConsole.WriteLine(“Dog barks”);
\n}
\n}<\/p>\n<\/div><\/div>11. How do you implement an interface in C#?<\/h3>
\nvoid Drive();
\n}
\nclass Car : IDriveable {
\npublic void Drive() {
\nConsole.WriteLine(“Driving a car”);
\n}
\n}<\/p>\n<\/div><\/div>12. What is the difference between an abstract class and an interface in C#?<\/h3>
\npublic abstract void MakeSound();
\n}
\ninterface IRun {
\nvoid Run();
\n}<\/p>\n<\/div><\/div>13. How do you handle exceptions in C#?<\/h3>
\nint result = 10 \/ 0;
\n} catch (DivideByZeroException ex) {
\nConsole.WriteLine(“Cannot divide by zero”);
\n} finally {
\nConsole.WriteLine(“End of try-catch block”);
\n}<\/p>\n<\/div><\/div>14. What is a delegate in C#, and how do you declare and use it?<\/h3>
\nPrintMessage pm = new PrintMessage(Console.WriteLine);
\npm(“Hello, Delegates!”);<\/p>\n<\/div><\/div>15. How do you implement a generic class in C#?<\/h3>
\npublic T Field;
\npublic GenericClass(T value) {
\nField = value;
\n}
\n}
\nGenericClass<int> myClass = new GenericClass<int>(10);<\/p>\n<\/div><\/div>16. How do you use LINQ to filter and sort a list of integers?<\/h3>
\nvar sortedNumbers = from n in numbers
\nwhere n > 2
\norderby n
\nselect n;<\/p>\n<\/div><\/div>17. What is the purpose of the List<T> class, and how do you add elements to it?<\/h3>
\nnumbers.Add(1);
\nnumbers.Add(2);<\/p>\n<\/div><\/div>18. How do you find the maximum value in a list using LINQ?<\/h3>
\nint maxValue = numbers.Max();<\/p>\n<\/div><\/div>19. What is the difference between IEnumerable and IQueryable in C#?<\/h3>
20. How do you group data using LINQ in C#?<\/h3>
\ngroup n by n % 2 into g
\nselect g;<\/p>\n<\/div><\/div>21. How do you read the contents of a file line by line in C#?<\/h3>
\nstring line;
\nwhile ((line = sr.ReadLine()) != null) {
\nConsole.WriteLine(line);
\n}
\n}<\/p>\n<\/div><\/div>22. What is the method to write text to a file in C#?<\/h3>
\nsw.WriteLine(“Hello, World!”);
\n}<\/p>\n<\/div><\/div>23. How do you check if a file exists in C#?<\/h3>
24. What is the method to copy a file from one location to another in C#?<\/h3>
25. How do you delete a file in C#?<\/h3>
26. What is an event in C#, and how do you declare one?<\/h3>
27. How do you subscribe to an event in C#?<\/h3>
28. What is a multicast delegate in C#?<\/h3>
\nNotify del = Method1;
\ndel += Method2;<\/p>\n<\/div><\/div>29. How do you remove a method from a delegate’s invocation list in C#?<\/h3>
30. How do you raise an event in C#?<\/h3>
\nMyEvent?.Invoke(this, EventArgs.Empty);
\n}<\/p>\n<\/div><\/div>31. How do you create a custom exception in C#?<\/h3>
\npublic MyCustomException(string message) : base(message) { }
\n}<\/p>\n<\/div><\/div>32. What is the difference between throw and throw ex in C#?<\/h3>
\n\/\/ Code that throws an exception
\n} catch (Exception ex) {
\nthrow; \/\/ Preserves stack trace
\n}<\/p>\n<\/div><\/div>33. How do you implement a try-finally block in C#?<\/h3>
\n\/\/ Code that may throw an exception
\n} finally {
\n\/\/ Code that always runs
\n}<\/p>\n<\/div><\/div>34. What is the purpose of the StackTrace class in C#?<\/h3>
\nConsole.WriteLine(st.ToString());<\/p>\n<\/div><\/div>35. How do you log exceptions in C#?<\/h3>
\n\/\/ Code that may throw an exception
\n} catch (Exception ex) {
\nFile.WriteAllText(“log.txt”, ex.ToString());
\n}<\/p>\n<\/div><\/div>36. How do you create a new thread in C#?<\/h3>
\nmyThread.Start();<\/p>\n<\/div><\/div>37. What is the Task class in C#, and how do you use it for asynchronous operations?<\/h3>
\n\/\/ Code to run asynchronously
\n});<\/p>\n<\/div><\/div>38. How do you use the async and await keywords in C#?<\/h3>
\nint result = await Task.Run(() => {
\n\/\/ Simulate long-running task
\nreturn 42;
\n});
\nreturn result;
\n}<\/p>\n<\/div><\/div>39. What is a ThreadPool, and how do you use it in C#?<\/h3>
\n\/\/ Code to run in the thread pool
\n});<\/p>\n<\/div><\/div>40. How do you implement a cancellation token to cancel an ongoing task in C#?<\/h3>
\nTask.Run(() => {
\nwhile (!cts.Token.IsCancellationRequested) {
\n\/\/ Long-running task
\n}
\n}, cts.Token);
\n\/\/ Cancel the task
\ncts.Cancel();<\/p>\n<\/div><\/div>41. How do you create a model class for a database table in Entity Framework?<\/h3>
\npublic int ProductId { get; set; }
\npublic string Name { get; set; }
\n}<\/p>\n<\/div><\/div>42. How do you perform a basic CRUD operation using Entity Framework?<\/h3>