C# Interview Questions and Answers for Beginner

Q1. What is an OOPS?

A1. Object oriented is a type of methodology used for building software application. It consists of classes, object and method.

Q2. What is a Data Type?

A2. Data Type defines the type of data that can be stored in a variable.

Q3. What is a compiler?

A3. The compiler is special programs that process the statement written in a particular programming language and convert them into machine language.

Q4. What is a Class?

A4. Class is a set of object that shares a common structure and behavior.

Q5. What is a Main () Function?

A5. Main () function is the entry point of the application.

Q6. What is an Object?

A6. An object is an instance of a class. We can create object to access member variables and member function of a class.

Q7. What is a Variable?

A7. A variable is a location in the memory that has a name and contains a value. The value would be integer, decimal or character.

Q8. Explain Types of Data Types?

A8.

Value Type: - Value type directly contains data. Ex. Char, int, float

Reference Type: - The reference type do not maintain data but they contain a reference to the variable, which are stored in memory. Ex. string

Q9. What is an Explicit Conversion?

A9. Converting one data type to the other data type is called the explicit conversion.

Q10. What is a Using Keyword?

A10. The using keyword is used to include the namespaces in the program.

Q11. What is the Comment Entry?

A11. Comment entry is a message for a programmer that describes a class, a method or a statement. The compiler does not execute a comment entry.

Q12. What is a function?

A12. Function is a set of statements that performance specific task in response to a message.

Q13. What is a Loop?

A13.  Loop structures are used to execute one or more lines of code repetitively.

Q14. What is an Abstraction?

A14. An abstraction is process of reducing information content in an order to retain only the relevant information for a particular purpose.

OR

An abstraction involves extracting only the relevant information.

Q15. What is an Encapsulation?

A15. An encapsulation is a process of hiding all the details of an object that do not contribute to its essential characteristics.

OR

An encapsulation involves packaging one or more component together.

Q16. What is an Access Specifier?

A16. An access specifier defines the scope of class member.

Q17. Explain Type of Access Specifiers?

A17.

Public - Access is not restricted.

Private - Access is limited to the containing type.

Protected - Access is limited to the containing class or types derived from the containing class.

Internal - Access is limited to the current assembly.

Protected Internal - Access is limited to the current assembly or types derived from the containing class.

Q18. What is a Method?

A18. A method is a set of one or more program statement, which can be executed by referring to the method name.

Q19. What is a Parameter?

A19. A parameter is place holders in a program that accept a user define values whenever the program is executed.

Q20. What is a Static Variable?

A20. Static variable are class variables it instantiated only once for a class at class load time. Static variable is a variable whose single copy in memory is shared by all objects. So any modification to the static variable will modify its value in all objects. It value remains constant for the entire class. It variable remains the same data throughout the execution of a program.

Q21. What is a Static Function?

A21. Static function is function which can access only static variables and we can invoke these methods without an instance of class, only using class name.

Q22. What is an Enumeration?

A22. An enumeration is a value type data type, which contains its own value and cannot inherit or cannot pass inheritance. Enumeration allows assigning symbolic names to integral constant.

Q23. What is an Array?

A23. An array is collection of value of same data type. An array is reference type variable.

Ex. string [] a = {"a","b","c"}; int [] b = {1, 2, 3};

Here a and b are store in heap. "a","b","c" and 1,2,3 are store in stack.

Q24. What is a Collection?

A24. Collections are class used to store arbitrary object in an organized manner.

Collection is a single object representing a group of object. The object in the collection is called element.

Q25. What is a Structure?

A25. A single variable hold the related data of various data type is called atructure.  It is a value type data type.

Q26. What is boxing?

A26. The conversion of value type to reference type variable is called boxing.

Q27. What is Unboxing?

A27. Unboxing means converting from reference type to value type is called unboxing.

Q28. What is a constructor?

A28. Constructor is a special type of method that is invoked when we create a new instance of class. It is used to initialize the member of the class. The name of a constructor is the same as the name of the class that contains it.

Q29. Explain the type of Constructor?

A29.

Instance constructors

An instance constructor is called whenever an instance of a class is created. These constructors are used to initialize data member of the class.

Static Constructor

Static constructors are used to initialize the static variable of a class. These variables are created using the static keyword and they store values that can be shared by all the instance of a class. These constructors have an implicit private access.  This constructors will be invoked only once during the execution of a program.

Q30. What is a Destructor?

A30. Destructors are special methods that are used to release the instance of a class from memory. A class can have only one destructor.

Q31. What is Garbage Collection?

A31. Garbage collection is a process that automatically frees the memory of object that is no more in use. Garbage collection only unreferenced object are destroyed.

Q32. What is a Polymorphism?

A32. The term polymorphism was derived from the Greek words ‘poly’ and ‘morphos’, which mean ‘many’ and ‘forms’ respectively. Polymorphism can either be static or dynamic. In static polymorphism the response to a function decided at compile time. In dynamic polymorphism the response to the function decided at run time.

Static Polymorphism

Function Overloading

Operator Overloading

Dynamic Polymorphism

Abstract classes

Virtual function

Q33. What is a Function Overloading?

A33. Function overloading is a process of using same name for two or more functions.

Q34. What is a Operator Overloading?

A34. Operator overloading provides additional capabilities to C# operators when are applied to user-defined data type.

Q35. What is a Function Signature?

A35. Passing different type of parameter, sequence of parameter, or number of parameters for a function is called function signature. The return type is not a part of function’s signature.

Q36. What is a Function Overriding?

A36. The subclass redefine the function of super class is called function overriding.

Q37. What is a Unary Operator?

A37. Unary operators are operators that act on a single operand. Ex. ++,--

Q38. What is a Binary Operator?

A38. Binary operators are operators that work with two operands. Ex. +=, -=, <, > etc.

Q39. What is an Inheritance?

A39. An inheritance is process of creating a new class by adding some features to an existing class is known as inheritance.

Q40. What is Base Class?

A40. The class from which attributes are derived is called the base class.

Q41. What is Derived Class?

A41. A class that inherits or derives attributes from another class is called the derived class.

Q42. What is an Abstract Class?

A42. An abstract class contains one or more abstract methods and can have non abstract methods. It cannot be initiated but they can be extended into sub classes. An abstract class is useful when there is common functionality implement in a super class.

Rule:-

Cannot create an instance of an abstract class.

Cannot declare an abstract method outside an abstract class.

Cannot be declared sealed.

Q43. What is a Sealed Class?

A43. Sealed class is a class which cannot be extended.

Q44. What is a Sealed Method?

A44. In C# a method can’t be declare sealed. However, when we override a method in derived class, we can declare the overridden method as sealed. By declaring it as sealed, we can avoid further overriding of this method.

Q45. What is an Interface?

A45. An interface defines the syntactical contract that all derived classes should follow. Interfaces contain only the declaration of member i.e. properties, method, and event.

Q46. What is different between an Abstract class and an Interface?

A46.

An Abstract class	An interface
A class extends only one abstract class	A class implements multiple interfaces
An abstract class is a class which contains one or more abstract methods which has to implement by sub classes.	An interface is a java object containing method declaration and doesn’t contain implementation. The classes which have implementing the interfaces must provide the method definition for all the methods.
An abstract class contains one or more abstract methods.	An interface contains all abstract method and final declaration
An abstract class contains method definition of the some methods	An interface contains only method declaration no definition provided
An abstract class are useful in a situation that some general method should be implemented and specialization behavior should be implemented by child class	An interface are useful in a situation that all properties should be implemented

Q47. What is a Stream?

A47. The stream is a sequence of byte travelling from a source to a destination over a communication path.

Q48. What is an Exception?

Q48. An exception is an erroneous situation that occurred during program execution. Exception situation arises when operation cannot be completed normally.

Q49. What is a Syntax Error?

A49. Syntax error occurs when compiler cannot compile code.

Q50. What is a Runtime error?

A50. Runtime error occurs when an application attempts to perform an operation which is not allowed at runtime. It is also called an exception.

Q51. What is a Logical error?

A51. Logical error occurs when an application compiles and runs properly but does not produce the expected results.

Q52. What is an Exception handling?

A52. An exception handling is a process of providing an alternative path of execution when the program is unable to execute as a desire.

Q53. What is a Thread?

A53. Thread is the execution path of a program used to run application that performed large and complex computation.

Q54. Define Thread Methods?

A54.

Start () - Start a thread.

Sleep () - makes the thread to pause for a period of time.

Abort () – Terminates the thread.

Suspend () – Suspend a thread. If thread is already suspended it has no effect.

Resume () – Resumes the suspended thread.

Q55. What is a Race Condition?

A55. When two or more thread simultaneously access a variable at least one thread tries to write a value in the variable.  This is called the race condition.

Q56. What is a Deadlock Condition?

A56. This condition arises in a computer system when two threads wait for each other to complete their operations before performing their individual action.

Q57. What is a Lock starvation?

A57. This limitation arises when the execution of a thread is postponed because of its low priority.

Q58. What is the disadvantage of multithreading?

A58. Race Condition, Deadlock Condition, and Lock starvation.

Q59. Define Thread Priority?

A59. Thread priority is the property that specifies the priority of one thread with respect to the priority of another thread.

Above normal

Below normal

Highest

Lowest

Normal

Q60. What is a Delegate?

A60. Delegate is a reference type variable, which holds the reference to a method. This reference can be change at runtime, as desired

Q61. Define Type of Delegates?

A61.

Single-cast Delegate

A single-cast delegate derives from the System.Delegate class. It contains reference to one method at a time.

Multicast Delegate

A multicast delegate derives from the System. MulticastDelegate class. It contains an invocation list of multiple methods.

Q62. What is an Event?

A62. An event is an action or occurrence, such as clicks, key presses, mouse movement, or system generated notification.

Q63. What is a Publisher?

A63. A publisher is an object that contains the definition of the event and the delegates.

Q64. What is a Subscriber?

A64. A subscriber is an object that wants to accept the event and provide a handler to the event.

Q65. What is an Attribute?

A65. An attribute is a declarative tag that is used to convey information to runtime about the behavior of programmatic element such as classes, enumerations, and assemblies. A declarative tag is depicted by square ([ ]) brackets placed above the definition of an element such as class or a method.  Ex. Conditional, WebMethod, DllImport, and Obsolete.

Q66. What is a Reflection?

A66. Reflection is used in the process of obtaining type of information at runtime.

Q67. What is a Common Language Runtime (CLR)?

A67. The CLR is one of the most essential components of the .NET Framework. CLR is the environment where all program using .NET technologies are executed. It provides service such as code compilation, memory allocation, and garbage collection. The CLR allows the execution of code across different platform by translating code into Intermediate Language (IL). IL is low level language that the CLR understands.

Q68. What is an Intermediate Language (IL)?

A68. IL is converted into machine language during execution by the Just-In-Time (JIT) compiler. During JIT compilation, code is also checked for type safety.

Q69. What is a Common Language Specification (CLS)?

A69. CLR consists of a set of common rules followed by all the languages of the .NET framework. This set of rules is known as a Common Language Specification (CLS). CLS enables an object or application to interact with the objects or application of other languages.

Q70. What is a Common Type System (CTS)?

A70. One of the specifications defined in CLS is Common Type System (CTS), which provides a type system that is common across all languages. CTS define how data type are declared, used, and managed in the code at run time.

The CTS also defines the rules that ensure that the data types of objects written in various languages are able to interact with each other.

Q71. What is a Managed Code?

A71. The code developed in .NET is called managed code.

Q72. What is a Namespaces?

A72. Namespaces is logical groups of related classes and interfaces, which can be used by any languages targeting the .NET Framework.

Q73. What is Assemblies?

A73. An assembly is the single (smallest) deployable unit that contains all the information about the implementation of classes, structures, and interfaces.

Q74. What is Metadata?

A74. The assembly stores all the information about itself. This information is called metadata and includes the name and version number of the assembly, security information about the dependencies, and a list of the files that constitute the assembly.

Q75. What is a pointer?

A75. Pointer is a variable that stores the memory address of another variable.

Q76. What is a package?

A76. Package is a group of sub packages, classes and interfaces.

Q77. What is an Assertion?

A77. An assertion is a way to test certain assumption about the logic of a program.

Q78. What is an identifier?

A78. An identifier is a name given to a class variable or method.

Q79. What is block or compound state?

A79.

Block is a group of statement that are correlated together.

OR

Compound statement is a group of statement bounded by opening or closing braces ({}).

Ex. Block.

Q80. What is a Final Class?

A80. Final class is a class which cannot be subclasses.

Q81. What is a Final Variable?

A81. Final variable is a variable which value is constant. Any attempt to change the value of final variable causes a compiler error.

Q82. What is Final Method?

A82. Final method is a method which cannot be overridden.

Q83. What is an Iterator?

A83. An iterator is an interface enables us to scan forward through any collection.

Q84. What is a Socket?

A84. Socket is the name given in one particular programming model to the endpoints of communication link between processes.

Q85. What is a Property?

A85. Properties are use to determine the appearance of various controls (items) at runtimes.

Q86. What is an Analysis?

A86. An analysis is the stage where users and developer of the system get together and arrive at a common understanding of system. The purpose of analysis is to provide a description (solution) of the problem.

Q87. What is Design?

A87. Design is the blue print of the system that to be implemented.

Q88. What is an Operator?

A88. An operator is a set of one or more characters that is used for computation or comparison.

Q89. What is a Pooling?

A89. Pooling is the process in which a single event is executed at a time.

Q90. What is a Client Id?

A90. A unique identification number used when sending data to a specific client.

Q91. What is a GUID?

A91. GUID stands for Global Unique Identifier. It’s generating random number of string each time.

Ex. System.Guid.NewGuid.ToString();

Q92. Class vs. Structure?

A92. Both can contain member such as fields and methods. Both require a constructor to create a new instance of them and like all type in the .NET Framework. Both inherit from object. The key difference between class and structure is that class is reference type and structure is value type. On a low level this means that the instance data for class is allocated on the heap, whereas the instance data for structure is allocated on the stack.

Note:-

Structure cannot have a parameter less constructors but he has parameterize constructors and also structure does not have destructor like class.

Q93. Different between String and StringBuilder?

A93.

String is immutable. It means that you can't modify string at all.

StringBuilder is mutable. It can be modified in any way and it doesn’t require creation of new instance. When work is done .ToString() can be called to get the string.

Q94. Const Vs Readonly Vs Static Keyword?

A94.

A const field requires a value to be provided at compile-time.	A readonly field cannot be assigned to (except in a constructor or a variable initializer)	A static variable is a variable that has been allocated statically whose lifetime Or "extent" extends across the entire run of the program.
Const field value cannot be change once assigned.

Q95. Var vs Dynamic keyword?

A95.

Var keyword provides compile time initialization.	Dynamic keyword provides runtime initialization.
Once you can initialize the type of value, you can’t change it.	You can initialize the type of value at runtime.
	You can re- initialize the dynamic variable.
Example var strA = 10; strA = "Hello"; Here, strA value assigned 10 i.e. strA containing an integer value. If you try to assigned the string value to strA variable you will get the following error. Cannot implicitly convert type 'string' to 'int'	Example dynamic strA = 10; strA = "Hello"; Here, strA value assigned 10 i.e. strA containing an integer value. If you change the value as string, dynamic variable behave as a string variable at runtime.

Q96. What is the “this” keyword?

A96. The this keyword refers to the current instance of the class and is also used as a modifier of the first parameter of an extension method.

Q97. What is the “base” keyword?

A97. The base keyword is used to access members of the base class from within a derived class.

Q98. What is the “extern” keyword?

A98. The extern modifier is used to declare a method that is implemented externally. A common use of the extern modifier is with the DllImport attribute when you are using Interop services to call into unmanaged code. In this case, the method must also be declared as static.