125 Basic C# Interview Questions and
Answers
Below is the list of 125 basic C#
interview questions with their answers. These C# interview questions
and answers are very simple and straight-forward which cover the
basic concepts of C# mostly related to object oriented concepts. So if you are
preparing for C# interview, I will suggest you to must go through these 125 C#
basic interview questions and answers to revise your C# concepts. Here goes the
list of 125 basic C# interview questions and answers.
1. What is C#?
C# (pronounced "C sharp")
is a simple, modern, object-oriented, and type-safe programming language. It
will immediately be familiar to C and C++ programmers. C# combines the
high productivity of Rapid Application Development (RAD) languages.
2. What are the types of comment in
C#?
There are 3 types of comments in C#.
Single line (//)
Multi (/* */)
Page/XML Comments (///).
3. What are the namespaces used in
C#.NET?
Namespace is a logical grouping of
class.
using System;
using System.Collections.Generic;
using System.Windows.Forms;
4. What are the characteristics of
C#?
There are several characteristics of
C# are :
Simple
Type safe
Flexible
Object oriented
Compatible
Consistent
Interoperable
Modern
5. What are the different categories
of inheritance?
Inheritance in Object Oriented
Programming is of four types:
Single inheritance: Contains one base class and one derived class.
Hierarchical inheritance: Contains one base class and multiple derived classes of the
same base class.
Multilevel inheritance: Contains a class derived from a derived class.
Multiple inheritance: Contains several base classes and a derived class.
6. What are the basic concepts of
object oriented programming?
It is necessary to understand some
of the concepts used extensively in object oriented programming.These include:
Objects
Classes
Data abstraction and encapsulation
Inheritance
Polymorphism
Dynamic Binding
Message passing.
7. Can you inherit multiple
interfaces?
Yes. Multiple interfaces may be inherited
in C#.
8. What is inheritance?
Inheritance is deriving the new
class from the already existing one.
9. Define scope?
Scope refers to the region of code
in which a variable may be accessed.
10. What is the difference between
public, static and void?
public: The keyword public is an access modifier that tells the C#
compiler that the Main method is accessible by anyone.
static: The keyword static declares that the Main method is a global
one and can be called without creating an instance of the class. The
compiler stores the address of the method as the entry point and uses this
information to begin execution before any objects are created.
void: The keyword void is a type modifier that states that the
Main method does not return any value.
11. What are the modifiers in C#?
Abstract
Sealed
Virtual
Const
Event
Extern
Override
Readonly
Static
New
12. What are the types of access
modifiers in C#?
Access modifiers in C# are :
public
protect
private
internal
internal protect
13. What is boxing and unboxing?
Implicit conversion of value type to
reference type of a variable is known as BOXING, for example integer to object
type conversion.
Conversion of reference type
variable back to value type is called as UnBoxing.
14. What is object?
An object is an instance of a class.
An object is created by using operator new. A class that creates an object in
memory will contain the information about the values
and behaviors (or methods) of that specific object.
15. Where are the types of arrays in
C#?
Single-Dimensional
Multidimensional
Jagged arrays.
16. What is the difference between
Object and Instance?
An instance of a user-defined type
is called an object. We can instantiate many objects from one class.
An object is an instance of a class.
17. Define destructors?
A destructor is called for a class
object when that object passes out of scope or is explicitly deleted.A
destructors as the name implies is used to destroy the objects that have
been created by a constructors.Like a constructor , the destructor is a member
function whose name is the same as the class name but
is precised by a tilde.
18. What is the use of enumerated
data type?
An enumerated data type is another
user defined type which provides a way for attaching names to numbers thereby
increasing comprehensibility of the code. The enum keyword automatically
enumerates a list of words by assigning them values 0,1,2, and so on.
19. Define Constructors?
A constructor is a member function
with the same name as its class. The constructor is invoked whenever an object
of its associated class is created.It is called constructor because it
constructs the values of data members of the class.
20. What is encapsulation?
The wrapping up of data and
functions into a single unit (called class) is known as encapsulation.
Encapsulation containing and hiding information about an object, such as
internal data structures and code.
21.Does c# support multiple
inheritance?
No,its impossible which accepts
multi level inheritance.
22. What is ENUM?
Enum are used to define constants.
23. What is a data set?
A DataSet is an in memory
representation of data loaded from any data source.
24. What is the difference between
private and public keyword?
Private: The private keyword is the default access level and most
restrictive among all other access levels. It gives least permission to a
type or type member. A private member is accessible only within the body of the
class in which it is declared.
Public: The public keyword is most liberal among all access levels,
with no restrictions to access what so ever. A public member is accessible
not only from within, but also from outside, and gives free access to any
member declared within the body or outside the body.
25. Define polymorphism?
Polymorphism means one name,
multiple forms. It allows us to have more than one function with the same name
in a program. It allows us to have overloading of operators so that an
operation can exhibit different behaviors in different instances.
26. What is Jagged Arrays?
A jagged array is an array whose
elements are arrays.
The elements of a jagged array can
be of different dimensions and sizes.
A jagged array is sometimes called
an array–of–arrays.
27. What is an abstract base class?
An abstract class is a class that is
designed to be specifically used as a base class. An abstract class contains at
least one pure virtual function.
28. How is method overriding
different from method overloading?
When overriding a method, you change
the behavior of the method for the derived class. Overloading a method simply
involves having another method with the same name within the class.
29. What is the difference between
ref & out parameters?
An argument passed to a ref
parameter must first be initialized. Compare this to an out parameter, whose
argument does not have to be explicitly initialized before being passed to
an out parameter.
30. What is the use of using
statement in C#?
The using statement is used to
obtain a resource, execute a statement, and then dispose of that resource.
31.What is serialization?
Serialization is the process of converting an object into a stream of
bytes.
De-serialization is the opposite process of creating an object from a stream
of bytes.
Serialization / De-serialization is
mostly used to transport objects.
32. What are the difference between
Structure and Class?
Structures are value type and
Classes are reference type
Structures can not have contractors
or destructors.
Classes can have both contractors
and destructors.
Structures do not support
Inheritance, while Classes support Inheritance.
33. What is difference between Class
And Interface?
Class is logical representation of object. It is collection
of data and related sub procedures with defination.
Interface is also a class containg methods which is not having any
definations.Class does not support multiple inheritance. But interface can
support.
34. What is Delegates?
Delegates are a type-safe,
object-oriented implementation of function pointers and are used in many
situations where a component needs to call back to the component that is
using it.
35. What is Authentication and
Authorization?
Authentication is the process of
identifying users. Authentication is identifying/validating the user against
the credentials (username and password).
Authorization performs after
authentication. Authorization is the process of granting access to those users
based on identity.
Authorization allowing access of
specific resource to user.
36. What is a base class?
A class declaration may specify a
base class by following the class name with a colon and the name of the base
class. omitting a base class specification is the same as deriving from
type object.
37. Can “this” be used within a
static method?
No ‘This’ cannot be used in a static
method. As only static variables/methods can be used in a static method.
38. What is difference between
constants, readonly and, static ?
Constants: The value can’t be changed.
Read-only: The value will be initialized only once from the
constructor of the class.
Static: Value can be initialized once.
39. What are the different types of
statements supported in C#?
C# supports several different kinds
of statements are
Block statements
Declaration statements
Expression statements
Selection statements
Iteration statements
Jump statements
Try catch statements
Checked and unchecked
Lock statement
40. What is an interface class?
It is an abstract class with public
abstract methods all of which must be implemented in the inherited classes.
41.What are value types and
reference types?
Value types are stored in the Stack.
Examples : bool, byte, chat,
decimal, double, enum , float, int, long, sbyte, short, strut, uint, ulong,
ushort.
Reference types are stored in the
Heap.
Examples : class, delegate,
interface, object, string.
42. What is the difference between
string keyword and System.String class?
String keyword is an alias for
Syste.String class. Therefore, System.String and string keyword are the same,
and you can use whichever naming convention you prefer. The String class
provides many methods for safely creating, manipulating, and
comparing strings.
43. What are the two data types
available in C#?
Value type
Reference type
44. What are the different types of
Caching?
There are three types of Caching:
Output Caching: stores the responses from an asp.net page.
Fragment Caching: Only caches/stores the portion of page (User Control)
Data Caching: is Programmatic way to Cache objects for performance.
45. What is the difference between
Custom Control and User Control?
Custom Controls are compiled code
(Dlls), easier to use, difficult to create, and can be placed in toolbox. Drag
and Drop controls.
Attributes can be set visually at
design time. Can be used by Multiple Applications (If Shared Dlls), Even if
Private can copy to bin directory of web application add reference and
use. Normally designed to provide common functionality independent of
consuming Application.
User Controls are similar to those
of ASP include files, easy to create, can not be placed in the toolbox and
dragged - dropped from it. A User Control is shared among the single
application files.
46. What is methods?
A method is a member that implements
a computation or action that can be performed by an object or class. Static
methods are accessed through the class. Instance methods are accessed
through instances of the class.
47. What is fields?
A field is a variable that is
associated with a class or with an instance of a class.
48. What is events?
An event is a member that enables a
class or object to provide notifications. An event is declared like a field
except that the declaration includes an event keyword and the type must be
a delegate type.
49. What is literals and their
types?
Literals are value constants
assigned to variables in a program. C# supports several types of literals are
Integer literals
Real literals
Boolean literals
Single character literals
String literals
Backslash character literals
50. What is the difference between value
type and reference type?
Value types are stored on the stack
and when a value of a variable is assigned to another variable.
Reference types are stored on the
heap, and when an assignment between two reference variables occurs.
51. What are the features of c#?
C# is a simple and powerful
programming language for writing enterprise edition applications.
This is a hybrid of C++ and VB. It
retains many C++ features in the area statements,expressions, and operators and
incorporated the productivity of VB.
C# helps the developers to easily
build the web services that can be used across the Internet through any
language, on any platform.
C# helps the developers
accomplishing with fewer lines of code that will lead to the fewer errors in
the code.
C# introduces the considerable
improvement and innovations in areas such as type safety,versioning. events and
garbage collections.
52. What are the types of errors?
Syntax error
Logic error
Runtime error
53. What is the difference between
break and continue statement?
The break statement is used to
terminate the current enclosing loop or conditional statements in which it
appears. We have already used the break statement to come out of switch
statements.
The continue statement is used to
alter the sequence of execution. Instead of coming out of the loop like the
break statement did, the continue statement stops the current iteration
and simply returns control back to the top of the loop.
54. Define namespace?
The namespace are known as
containers which will be used to organize the hierarchical set of .Net classes.
55. What is a code group?
A code group is a set of assemblies
that share a security context.
56. What are sealed classes in C#?
The sealed modifier is used to
prevent derivation from a class. A compile-time error occurs if a sealed class
is specified as the base class of another class.
57. What is the difference between
static and instance methods?
A method declared with a static
modifier is a static method. A static method does not operate on a specific
instance and can only access static members.
A method declared without a static
modifier is an instance method. An instance method operates on a specific
instance and can access both static and instance members. The instance on
which an instance method was invoked can be explicitly accessed as this. It is
an error to refer to this in a static method.
58. What are the different types of
variables in C#?
Different types of variables used in
C# are :
static variables
instance variable
value parameters
reference parameters
array elements
output parameters
local variables
59. What is meant by method
overloading?
Method overloading permits multiple
methods in the same class to have the same name as long as they have unique
signatures. When compiling an invocation of an overloaded method, the
compiler uses overload resolution to determine the specific method to invoke.
60. What is parameters?
Parameters are used to pass values
or variable references to methods. The parameters of a method get their actual
values from the arguments that are specified when the method is invoked.
There are four kinds of parameters: value parameters,
reference parameters, output parameters, and parameter arrays.
61. Is C# is object oriented?
Yes, C# is an OO langauge in the
tradition of Java and C++.
62. What is the difference between
Array and Arraylist?
An array is a collection of the same
type. The size of the array is fixed in its declaration. A linked list is
similar to an array but it doesn’t have a limited size.
63. What are the special operators
in C#?
C# supports the following special
operators.
is (relational operator)
as (relational operator)
typeof (type operator)
sizeof (size operator)
new (object creator)
.dot (member access operator)
checked (overflow checking)
unchecked (prevention of
overflow checking)
64. What is meant by operators in
c#?
An operator is a member that defines
the meaning of applying a particular expression operator to instances of a
class. Three kinds of operators can be defined: unary operators, binary
operators, and conversion operators. All operators must be declared as public
and static.
65. What is a parameterized type?
A parameterized type is a type that
is parameterized over another value or type.
66. What are the features of
abstract class?
An abstract class cannot be
instantiated, and it is an error to use the new operator on an abstract class.
An abstract class is permitted (but
not required) to contain abstract methods and accessors.
An abstract class cannot be scaled.
67. What is the use of abstract
keyword?
The modifier abstract is a keyword
used with a class, to indicate that this class cannot itself have direct
instances or objects, and it is intended to be only a 'base' class to
other classes.
68. What is the use of goto
statement?
The goto statement is also included
in the C# language. This goto can be used to jump from inside a loop to
outside. But jumping from outside to inside a loop is not allowed.
69. What is the difference between
console and window application?
A console application, which is
designed to run at the command line with no user interface.
A Windows application, which is
designed to run on a user’s desktop and has a user interface.
70. What is the use of return
statement?
The return statement is associated
with procedures (methods or functions). On executing the return statement, the
system passes the control from the called procedure to the calling
procedure. This return statement is used for two purposes :
to return immediately to the caller
of the currently executed code
to return some value to the caller
of the currently executed code.
71. What is the difference between
Array and LinkedList?
Array is a simple sequence of
numbers which are not concerned about each others positions. they are
independent of each others positions. adding,removing or modifying any
array element is very easy. Compared to arrays ,linked list is a comlicated
sequence of numbers.
72. Does C# have a throws clause?
No, unlike Java, C# does not require
the developer to specify the exceptions that a method can throw.
73. Does C# support a variable
number of arguments?
Yes, uisng the params keyword. The
arguments are specified as a list of arguments of a specific type.
74. Can you override private virtual
methods?
No, private methods are not
accessible outside the class.
75. What is a multi cast delegates?
Each delegate object holds reference
to a single method. However, it is possible for a delegate object to hold
references of and invoke multiple methods. Such delegate objects are
called multicast delegates or combinable delegates.
76. Which is an exclusive feature of
C#?
Xml documentation.
77. Is using of exceptions in C#
recommended?
Yes, exceptions are the recommended
error handling mechanism in .NET Framework.
78. What does a break statement do
in switch statements?
The break statement terminates the
loop in which it exists. It also changes the flow of the execution of a
program.
In switch statements, the break
statement is used at the end of a case statement. The break statement is
mandatory in C# and it avoids the fall through of one case statement to
another.
79. Is C# object oriented?
Yes, C# is an OO language in the
tradition of java and C++.
80. What is smart navigation?
The cursor position is maintained
when the page gets refreshed due to the server side validation and the page
gets refreshed.
81. What is the difference between
CONST and READONLY?
Both are meant for constant values.
A const field can only be initialized at the declaration of the field. A
readonly field can be initialized either at the declaration or.
82. Does C# have a throws clause?
No, unlike Java, C# does not require
(or even allow) the developer to specify the exceptions that a method can throw.
83. What are the different ways a
method can be overloaded?
Different parameter data types,
different number of parameters, different order of parameters.
84. Do events have return type?
No, events do not have return type.
85. What is event?
An event is an action performed
based on another method of the program.
An event is a delegate type dass
member that is used by an object or a class to provide a notification to other
objects that an event has occurred.
An event can be declared with the help
of the event keyword.
86. What is an identifier?
Identifiers are nothing but names
given to various entities uniquely identified in a program.
87. What are the different types of
literals in C#?
Boolean literals: True and False are literals of the Boolean type that map
to the true and false state, respectively.
Integer literals: Used to write values of types Int, ulnt, long, and ulong.
Real literals: Used to write values of types float, double, and dedmal.
Character literals: Represents a single character and usually consists of a
character in quotes, such as 'a'.
String literals: C# supports two types of string literals, regular string
literal and verbatim string literals. A regular string literal consists
of zero or more characters enclosed in double quotes, such as
"116110". A verbatim string literal consists of an @ character
followed by a double–quote character, such as ©"hello".
The Null literal: Represents the null–type.
88. What is meant by data
encapsulation?
Data encapsulation, also referred to
as data hiding, is the mechanism whereby the implementation details of a class
are kept hidden from the user. The user can only perform a restricted set
of operations on the hidden members of the class by executing
special functions called methods.
89. Can you override private virtual
methods?
No. Private methods are not
accessible outside the class.
90. What is the main difference
between a subprocedure and a function?
Subprocedures do not return a value,
while functions do.
91. How does C# differ from C++?
C# does not support #include
statement. It uses only using statement.
In C# , class definition does not
use a semicolon at the end.
C# does not support multiple code
inheritance.
Casting in C# is much safer than in
c++.
In C# switch can also be used on
string values.
Command line parameters array behave
differently in C# as compared to C++.
92. What is nested class?
A Nested classes are classes within
classes.
A nested class is any class whose
declaration occurs within the body of another class or interface.
93. Can you have parameters for
static constructors?
No, static constructors cannot have
parameters.
94. Is String is Value Type or
Reference Type in C#?
String is an object(Reference Type).
95. Does C# provide copy constructor?
No, C# does not provide copy
constructor.
96. Can a class or a struct have
multiple constructors?
Yes, a class or a struct can have
multiple constructors. Constructors in C# can be overloaded.
97. Can you create an instance of an
interface?
No, you cannot create an instance of
an interface.
98. Can an Interface contain fields?
No, an Interface cannot contain
fields.
99. Can a class have static
constructor?
Yes, a class can have static
constructor. Static constructors are called automatically, immediately before
any static fields are accessed, and are generally used to initialize
static class members. It is called automatically before the first instance is
created or any static members are referenced. Static constructors are called
before instance constructors. An example is shown below.
100. What is the main use of
delegates in C#?
Delegates are mainly used to define
call back methods.
101. What is the difference between
Shadowing and Overriding?
Overriding redefines only the implementation
while shadowing redefines the whole element.
In overriding derived classes can
refer the parent class element by using "ME" keyword, but in
shadowing you can access it by "MYBASE".
102. Can events have access
modifiers?
Yes, you can have access modifiers
in events. You can have events with the protected keyword, which will be
accessible only to inherited classes. You can have private events only for
objects in that class.
103. Why is the virtual keyword used
in code?
The Virtual keyword is used in code
to define methods and the properties that can be overridden in derived classes.
104. What are constructors and
destructors?
Constructors and destructors are
special methods.
Constructors and destructors are
special methods of every class.
Each class has its own constructor
and destructor and are called automatically when the instance of a class is
created or destroyed.
The constructor initializes all
class members whenever you access the class and the destructor destroys them
when the objects are not required anymore.
105. How can we suppress a finalize
method?
GC.SuppressFinalize()
106. Does C# support a variable
number of arguments?
Yes, using the params keyword.
The arguments are specified as a
list of arguments of a specific type, e.g., int. For ultimate flexibility, the
type can be object.
The standard example of a method
which uses this approach is System.console.writeLine().
107.Which method will you call to
start a thread?
Start
108. What is Generic?
Generic help us to create flexible
strong type collection.
Generic basically seperate the logic
from the datatype in order maintain better reusability, better maintainability
etc.
109. What are the different types of
polymorphism?
There are two types of polymorphism.
They are:
Compile time Polymorphism
Run time Polymorphism
110. What is the difference between
compile time polymorphism and run time polymorphism?
Compile time Polymorphism
Compile time Polymorphism also known
as method overloading.
Method overloading means having two
or more methods with the same name but with different signatures.
Run time Polymorphism
Run time Polymorphism also known as
method overriding.
Method overriding means having two
or more methods with the same name , same signature but with different
implementation.
111. Which namespace enables
multithreaded programming in XML?
System.Threading
112. Can we declare a block as
static in c#?
No, because c# doesnot support
static block, but it supports static method.
113. Can we declare a method as
sealed?
In C# a method can't be declared as
sealed. However when we override a method in a derived class, we can declare
the overridden method as sealed. By declaring it as sealed, we can avoid
further overriding of this method.
114. What Command is used to
implement properties in C#?
get & set access modifiers are
used to implement properties in c#.
115. What is static member?
The member defined as static which
can be invoked directly from the class level, rather than from its instance.
116. What is the syntax to inherit
from a class in C#?
When a class is derived from another
class, then the members of the base class become the members of the derived
class.
The access modifier used while
accessing members of the base class specifies the access status of the base
class members inside the derived class.
The syntax to inherit a class from
another class In C# is as follows:
class MyNewClass : MyBaseClass
117. What is a basic difference
between the while loop and do while loop in C#?
The while loop tests its condition
at the beginning, which means that the enclosed set of statements run for zero
or more number of times if the condition evaluates to true. The do while
loop iterates a set of statements at least once and then checks the condition
at the end.
118. What is the main difference
between a subprocedure and a function?
Subprocedures do not return a value,
while functions do.
119. What are sealed classes in c#?
The sealed modifier is used to
prevent derivation from a class.
A compile time error occurs if a
sealed class is specified as the base class of another class.
120. What is the difference between
class and an Interface?
Abstract classes can have
implementations for some of its members, but the interface can't have implementation
for any of its members.
Interfaces cannot have fields where
as an abstract class can have fields.
An interface can inherit from
another interface only and cannot inherit from an abstract class, where as an
abstract class can inherit from another abstract class or another
interface.
A class can inherit from multiple
interfaces at the same time, where as a class cannot inherit from multiple
classes at the same time.
Abstract class members can have
access modifiers where as interface members cannot have access modifiers.
121. What is the difference between
an abstract method & virtual method?
An Abstract method does not provide
an implementation and forces overriding to the deriving class (unless the
deriving class also an abstract class), where as the virtual method has an
implementation and leaves an option to override it in the deriving class. Thus
Virtual method has an implementation & provides the derived class with
the option of overriding it. Abstract method does not provide an implementation
& forces the derived class to override the method.
122. What is Static Method?
It is possible to declare a method
as Static provided that they don't attempt to access any instance data or other
instance methods.
123. What is a New modifier?
The new modifier hides a member of
the base class. C# supports only hide by signature.
124. What are the advantages of get
and set properties in C#?
The get property accessor is used to
return the property value.
The set property accessor is used to
assign a new value.
125. What are the difference between
const and read-only?
A const cannot be static, while read-only
can be static.
A const need to be declared and
initialized at declaration only, while a read-only can be initialized at
declaration or by the code in the constructor.
A const's value is evaluated at
design time, while a readonly's value is evaluated at runtime.
