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C# (Sharp) Interview Questions And Answers

SOOPRO Pathshala provides C# Interview Questions and Answers

1. What is C#?

C# is pronounced "C-Sharp". It is an object-oriented programming language created by Microsoft that runs on the .NET Framework.

2. What is the role of C#?

The role of C# as a programming language is used to create desktop apps, mobile apps, web apps, websites, and web services.

3. What is meant by object-oriented programming?

Object-oriented programming (OOP) is a computer programming model that organizes software design around data, or objects, rather than functions and logic.

OOPs is based on following principles

  • Abstraction
  • Encapsulation
  • Inheritance
  • Polymorphism

4. What is the difference between managed and unmanaged code?

Managed code is executed by the Common Language Runtime (CLR) of the .NET Framework.

unmanaged code is executed by the Operating System (OS).

5. How is C# different from C??

C# is an object-oriented programming language, whereas C is a procedural programming language.

C# is used for desktop and mobile apps as well as services, where as C is best suited for hardware apps and system programming.

C#has 87 keywords, where as C draws on just 32 different keywords.

6. What is an object in C#?

An object is a real-world entity.

7. What is a class in C#?

A class is a user-defined blueprint architecture, which is used to contains data members and member functions.

8. What is a method in C#?

A method is a set of statements which perform some action.

9. What is meant by structure in C#?

In C#, a structure is a composite type of data consisting of various data types, including methods, fields, constructors, constants, properties, indexers, operators, and even other structures.

10. How is code compiled in C#?

When a project is developed, C# source code is compiled into Intermediate Language (IL). IL is a set of instructions that further converted by JIT compiler to machine code.

11. What is file handling in C#?

File handling is the process of saving information to the disk of external storage. The saved file contains bytes of data and is available for retrieval at a later date.

12. What is the purpose of control statements in C#?

Control statements are used to control the flow of execution of program.

13. What is meant by garbage collection in C#?

Garbage collection is the process of managing memory in an application. The garbage collector automatically disposes of memory that is no longer used to make memory available for new allocations.

14. What is a constructor in C#?

A constructor is a special method of a class or structure that initializes data members or object of class

15. What is a destructor in C#?

Destructor is an instance member function that is invoked automatically whenever an object is going to be destroyed. Destructors are also referred to as finalizers.

16. What is an array in C#?

An array is a collection of similar elements.

17. What is a constant in c#?

Constants are fixed values that cannot be modified or changed.

18. What is an indexer in C#?

C# indexers are usually known as smart arrays.

19. What are the different types of classes in C#?

There are four types of classes in C#.

1. Abstract classes: These provide a common definition for a base class that other classes can be derived from

2. Static classes: These contain static items that can only interact with other static items.

3. Partial classes:These are portions of a class that a compiler can combine to form a complete class

4. Sealed classes:These cannot be inherited by any class but can be instantiated

20. What are circular references in C#?

Circular references, also known as circular dependencies, occur when two or more components, classes, namespaces, or projects depend on each other directly or indirectly.

21. What is meant by object pooling in C#?

Object pooling is a memory optimization technique that reduces the overhead of creating and destroying objects frequently

22. What are the different types of control statements in C#?

There are generally considered to be three main types of control statements

1. Conditional statements which enable you to branch to different sections of code

2. Looping statementswhich enable you to loop through connections or perform the same series of operations repeatedly until a specified condition is met

3. Jump statementswhich enable control of flow to be shifted to another section of code

23. What is method overloading in C#?

Defining multiple methods having same name with different signatures in a same class is called method overloading.

Method overloading improves the readability of the program by reducing the number of names associated with a specific action.

24. What are boxing and unboxing in C#?

Boxing is used to convert a value type to a reference type.

Unboxing is used to convert a reference type to a value type.

25. What is the difference between ref and out keywords in C#?

The ref keyword is used when you want to pass a variable by reference to a method.

The out keyword is used when you want to pass a variable to a method for output purposes

26. What is Extension method in C#?

Extension methods allow you to inject additional methods without modifying, deriving or recompiling the original class, struct or interface.

27. What is the benefit of using namespace in c#

Namespaces in C# are used to organize too many classes so that it can be easy to handle the application.

28. When should nullable types be used in C#?

Nullable types are used to represent an undefined value of an underlying type. It essentially means ‘no value’ and is generally used when no data is available for the field.

29. How is serialization implemented in C#?

In C#, serialization is the process of converting an object into a stream of bytes for storage on a memory, database, or file.

30. What is the difference between String and StringBuilder in C#? Sample answer:

A string object is immutable, meaning that it cannot be changed after it’s created.

A string builder object is mutable and can be modified as the developer sees fit.

31. How is reflection used in C#?

In C#, reflection is used to obtain metadata on types at runtime. In other words, it allows developers to retrieve data on the loaded assemblies and the types within them.

It’s implemented using a two-step process. First, you get the type object. Second, you use the type to browse members, such as methods and properties.

32. What are the advantages of generics in C#?

In C#, generics allow the developer to define classes and methods which can be used with specific data type. This brings several benefits:

  • Saves time by reusing code
  • Provides type safety without unnecessary overhead
  • Removes the need for boxing and unboxing
  • Generic collection types generally perform better with value types because there is no need to box the values

33. What are the disadvantages of generics in C#?

There are a few limitations with generics. These include:

  • They cannot be used with enumerations
  • They cannot be used with lightweight dynamic methods
  • The .NET framework doesn’t support context-bound generic types

34. What are the key differences between Array and ArrayList in C#?

An ArrayList has wider usage than an Array. The key differences include:

An Array is strongly-typed, meaning it only stores the same type of data.
An ArrayList is a non-generic collection type, meaning it can store multiple types of data

An Array stores a fixed number of elements.
An ArrayList features a variable number of elements and can continually be added to

An Array cannot accept null values, whereas an ArrayList can

35. How are the different types of control statements used in C#?

Each type of control statement has its own set of syntax used to invoke the statement:

1. Conditional statements include if- else, switch-case
2. Iteration statements include for, while, do-while and foreach
3. Jump statements include break, continue, return, and goto

36. When should multithreading be used and when should it be avoided in C#?

Multithreading, or threading, can be a good way to improve the performance of a program where several operations run simultaneously.

37. What is a multicast delegate in C#?

A multicast delegate in C# references multiple target methods. When a multicast delegate is used, all the functions the delegate is pointing to are invoked.

38. How would you explain the four fundamental concepts of object-oriented programming?

The four fundamental concepts of object-oriented programming can be explained as follows:

Encapsulation is used to show non essential feature and hide essential feature.

Polymorphism is the ability of a type to take on many forms using a single interface

Abstraction is used to show essential part and hide non essential part.

Inheritance is the process where one class derives (or inherits) its attributes and methods from another

39. How is the singleton design pattern implemented in C#?

In this pattern, a class has only one instance in the program that provides a global point of access to it.

This design pattern can be implemented in a number of ways, using:
Private and parameterless single constructor
Sealed class
Static variable to hold a reference to the single created instance

40. What is the difference between late binding and early binding in C#?

Early binding occurs at compile-time, whereas late binding occurs at runtime

42. When is method overriding used in C#?

If derived class defines same method as defined in its base class, it is known as method overriding in C#. It is used to achieve runtime polymorphism.

43. What is the difference between Const and ReadOnly keywords in C#?

There are several differences between Const and ReadOnly keywords in C#. These include:

ReadOnly is a constant used at runtime, whereas Const is a constant used at compile-time.
ReadOnly values can be changed, whereas Const values cannot be changed.
ReadOnly cannot be declared inside the method, whereas Const can

44. What is operator in c#?

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations.

45. What is meant by dependency injection in C#?

Dependency Injection (DI) is a software design pattern that helps developers build better software. It allows us to develop loosely-coupled code that is easy to maintain.

46. How can circular references be fixed in C#?

To handle the problem of circular references in C#, you should use garbage collection.

47. What is static class in C#?

In C#, a static class is a class that cannot be instantiated.

48. What are the different techniques for overloading a method in C#?

Method overloading can be achieved in the three following ways:

  • By using different data types of parameters in a method
  • By changing the number of parameters in a method
  • By changing the order of parameters in a method

49. How is exception handling performed in C#?

In C#, exception handling helps detect errors in code at runtime. The process is implemented using four different keywords:

1. Try identifies blocks of code where exceptions are activated.
2. Catch catches the exceptions that have been identified by Try
3. Finally executes a given set of statements depending on whether an exception is thrown out or not
4. Throw A program throws an exception when a problem shows up. This is done using a throw keyword.

50. What is the difference between a throw exception and a throw clause in C#?

Throw exception generally refers to the action of explicitly raising or generating an exception within your code.

Throw clause typically refers to the part of a method signature that indicates which exceptions can be thrown by that method

51. What is the difference between Interface and Abstract Class in C#?

Interface - An interface in C# defines a contract for classes that implement it. It is a purely abstract concept and can only contain method, property, event, or indexer declarations.
Interfaces cannot contain any implementation code. Classes that implement an interface must provide concrete implementations for all the members declared in the interface.

An abstract class in C# is a class that cannot be instantiated on its own and is meant to serve as a base or blueprint for other classes.

52. What is an enum in C#?

The enum keyword is used to declare an enumeration. It is a primitive data type that is user-defined.

53. What is the difference between “continue” and “break” statements in C#?

Using a break statement, you can 'jump out of a loop,' whereas using a continue statement, you can 'jump over one iteration' and resume your loop execution.

54. What are properties in C#?

A property is a member of a class that provides a way to read, write or compute the value of a private field.

55. What is the difference between Dispose and Finalize in C#?

The Dispose method releases unmanaged resources, such as file handles or database connections, not automatically managed by the .NET runtime.

The Finalize method is used to perform cleanup operations on an object just before it is garbage collected. Therefore, it is typically implemented in a class that overrides the Object.Finalize method.

56. What is c#?

C# is an object-oriented, modern programming language that was created by Microsoft. It runs on the .NET Framework.

57. What is garbage collection in C#?

Garbage collection in C# is an automatic memory management process that helps to release memory used by objects that are no longer needed by the application. .

58. What is the difference between a struct and a class in C#?

A class is a user-defined blueprint or prototype from which objects are created. Basically, a class combines the fields and methods(member function which defines actions) into a single unit.

A structure is a collection of variables of different data types under a single unit. It is almost similar to a class because both are user-defined data types and both hold a bunch of different data types

59. What is New Keyword in c#?

The new keyword is to create instances of classes (objects). It allocates memory for the object

60. What is Reflection in C#?

Reflection is the process of describing the metadata of types, methods, and fields in a code.

61. What is the difference between constant and read-only in C#?

A constant in C# is a value that is known at compile-time and remains unchanged throughout the program's execution
A read-only variable in C# is a variable whose value can be assigned at runtime, typically within a constructor, and once assigned, it cannot be changed.

62. What is the difference between to dispose and finalize methods in C#?

The primary difference between dispose() and finalize() is that the dispose() must be explicitly invoked by the user and the finalize() is called automatically by the garbage collector when the object is destroyed.

63. What are delegates in C#?

A delegate is a reference type variable that holds the reference to a matching method.


64. What are sealed classes in C#?

Sealed classes are used to restrict the users from inheriting the class

65. What is a multicasting delegate in C#?

Multicasting of delegate is an extension of the normal delegate. It helps the user to point more than one method in a single call.

66. What is a Virtual Method in C#?

In C# virtual method is a strategy that can be reclassified in derived classes A virtual method is declared in the parent class that can be overridden in the child class.

67. What is Multithreading with .NET?

Multi-threading is a process that contains multiple threads within a single process.

68. What is a Hash table class in C#?

The Hashtable class represents a collection of key/value pairs that are organized based on the hash code of the key.

69. What is LINQ in C#?

LINQ is known as Language Integrated Query and it is introduced in .NET 3.5 and Visual Studio 2008.
The beauty of LINQ is it provides the ability to .NET languages(like C#, VB.NET, etc.) to generate queries to retrieve data from the data source.

70. Why a private virtual method cannot be overridden in C#?

Because private virtual methods are not accessible outside the class.

71. What is Singleton design pattern in C#?

Singleton design pattern in C# is a common design pattern. In this pattern, a class has just one in

72. How to implement a singleton design pattern in C#?

We can implement a singleton design pattern in C# using:

  • No Thread Safe Singleton.
  • Thread-Safety Singleton.
  • Thread-Safety Singleton using Double-Check Locking.
  • Thread-safe without a lock.
  • Using .NET 4’s Lazy T type.

73. What are Events?

An event is a notification that generate when some action or changes occur.

74. What is the difference between Array and ArrayList?

Array is a fixed-size data structure that holds elements of the same data type.
ArrayList is dynamic array and grows automatically when new items are added to the collection.

75. Difference between SortedList and SortedDictionary in C#.

SortedListis implemented as an array of key-value pairs, where the keys are stored in a sorted order.

SortedDictionary is a collection class that provides a dynamically resizable data structure for storing key-value pairs, where the keys are sorted in a specific order

76. Explain types of comment in C# with examples

Single line
Multi line

77. What is an object?

An object is an instance of a class through which we access the methods of that class

78. What is Constructor?

A constructor is a member function in a class that has the same name as its class. The constructor is automatically invoked whenever an object class is created.

79. What is Jagged Arrays?

Jagged array is a container of other arrays. No. of rows in jagged called no. of arrays.

80. What is serialization?

The process of converting an object into a stream of bytes is called Serialization

81. Can we use “this” command within a static method?

We can’t use ‘This’ in a static method because we can only use static variables/methods in a static method.

82. What are value types and reference types?

A value type holds a data value within its own memory space. Reference type stores the address of the Object where the value is being stored. It is a pointer to another memory location.

83. What is method overloading?

Method overloading is creating multiple methods with the same name with different signatures in the same class.

84. Describe the accessibility modifier “protected internal”.

Protected Internal are accessible within the all classes of same application and in child class of other application.

85. What is the difference between method overriding and method overloading?

Method Overriding that enables a subclass to provide a specific implementation for a method that is already defined in its superclass.

Method overloading is a process of creating multiple methods with the same name having different signatures within same class.

86. What are the different ways a method can be overloaded?

Methods can be overloaded using different data types for a parameter, different order of parameters, and different number of parameters.

87. What is difference between “is” and “as” operators in c#?

is operator is used to check the compatibility of an object with a given type, and it returns the result as Boolean.

as operator is used for casting of an object to a type or a class.

88. Difference between .dll and .exe file

.dll: DLLs cannot be executed directly. They need to be referenced by other programs (usually EXE files) that use the functionality provided by the DLL.

.exe: EXE files are executable and can be run directly by the operating system

89. What is Console application?

A console application is an application that can be run in the command prompt in Windows

90. What is namespace in C#?

A namespace used to organize and group related classes, interfaces, structs, enums, and other types into a hierarchical structure.

91. What is keyword in c#?

A keyword is a reserved word that has a predefined meaning and purpose in the programming language.

92. What is variable in c#?

A variable is a named storage location that holds a value of a specific data type.

93. What is method in c#?

A method is a block of code that performs a specific task or operation.

94. what is atribute in c#?

An attribute is a declarative tag that provides additional information about an element in your code, such as a class, method, property, parameter, or assembly.

95. What is typecasting in c#?

Type casting in C# refers to converting one data type to another.

96. What is assembly in c#?

An assembly is the primary building block of a .NET Framework application. It is an Output Unit. Assemblies contain MSIL code.

98. what is data type in c#?

A data type specifies the type of data that a variable can store such as integer, floating, character etc.

99. what is loop?

Loops are used to execute one or more statements multiple times until a specified condition is fulfilled.

100. what are the types of loops in c#

There are four types of loops in c#

  • for
  • while
  • do while
  • foreach