C# Interview Question C#
Interview Questions have been designed specially to get you acquainted with the
nature of questions you may encounter during your interview for the subject
of C#. As per my experience good interviewers hardly plan to ask
any particular question during your interview, normally questions start with
some basic concept of the subject and later they continue based on further
discussion and what you answer −
What is C#?
C# is a modern, general-purpose, object-oriented
programming language developed by Microsoft. C# is designed for Common Language
Infrastructure (CLI), which consists of the executable code and runtime
environment that allows use of various high-level languages on different
computer platforms and architectures.
What is Jagged Array in C#?
A Jagged array is an array of arrays.
You can initialize a jagged array as −
int[][] scores = new int[2][]{new int[]{92,93,94},new int[]{85,66,87,88}};
Where, scores is an array of two arrays of
integers - scores[0] is an array of 3 integers and scores[1] is an array of 4
integers.
In how many ways you can pass
parameters to a method?
There are three ways that parameters can be
passed to a method −
·
Value
parameters − This method
copies the actual value of an argument into the formal parameter of the
function. In this case, changes made to the parameter inside the function have
no effect on the argument.
·
Reference
parameters − This method
copies the reference to the memory location of an argument into the formal
parameter. This means that changes made to the parameter affect the argument.
·
Output
parameters − This method
helps in returning more than one value.
Can you return multiple values from
a function in C#?
Yes! Using output parameters. A return statement
can be used for returning only one value from a function. However, using output
parameters, you can return two values from a function.
What is the difference between ref
and out parameters?
Output parameters are similar to reference parameters,
except that they transfer data out of the method rather than into it. Reference
parameter copies the reference to the memory location of an argument into the
formal parameter. This means that changes made to the parameter affect the
argument.
What is namespace in C#?
A namespace is designed for providing a way to
keep one set of names separate from another. The class names declared in one
namespace does not conflict with the same class names declared in another.
What is the purpose of using statement
in C#?
using keyword is used to include a namespace in
the program. A program generally has multiple using statements.
What are value types in C#
Value type variables can be assigned a value
directly. They are derived from the class System.ValueType.
The value types directly contain data. Some
examples are int, char, and float, which stores numbers, alphabets, and
floating point numbers, respectively. When you declare an int type, the system
allocates memory to store the value.
What are reference types in C#
The reference types do not contain the actual
data stored in a variable, but they contain a reference to the variables.
In other words, they refer to a memory location.
Using multiple variables, the reference types can refer to a memory location.
If the data in the memory location is changed by one of the variables, the
other variable automatically reflects this change in value. Example of built-in
reference types are: object, dynamic, and string.
Which class acts as a base class for
all the data types in .net?
The Object Type is the ultimate base class for
all data types in C# Common Type System (CTS). Object is an alias for
System.Object class. The object types can be assigned values of any other
types, value types, reference types, predefined or user-defined types. However,
before assigning values, it needs type conversion.
What is boxing in C#?
When a value type is converted to object type,
it is called boxing.
What is unboxing in C#?
When an object type is converted to a value
type, it is called unboxing.
What are dynamic type variables in
C#What is the difference between dynamic type variables and object type
variables?
Dynamic types are similar to object types except
that type checking for object type variables takes place at compile time, whereas
that for the dynamic type variables takes place at run time.
What are pointer types in C#?
Pointer type variables store the memory address
of another type. Pointers in C# have the same capabilities as the pointers in C
or C++.
Syntax for declaring a pointer type is −
type* identifier;
For example
char*
cptr;
int*
iptr;
What is the purpose of is operator
in C#?
is operator determines whether an object is of a
certain type.
If( Ford is Car) // checks if Ford is an object
of the Car class.
What is the purpose of as operator
in C#?
as operator casts without raising an exception
if the cast fails.
Object obj = new StringReader("Hello");
StringReader r = obj as StringReader;
What is encapsulation?
Encapsulation is defined 'as the process of
enclosing one or more items within a physical or logical package'.
Encapsulation, in object oriented programming methodology, prevents access to
implementation details.
How encapsulation is implemented in
C#?
Encapsulation is implemented by using access
specifiers.
What is the purpose of an access
specifier in C#?
An access specifier defines the scope and
visibility of a class member.
What is scope of a public member
variable of a C# class?
Public access specifier allows a class to expose
its member variables and member functions to other functions and objects. Any
public member can be accessed from outside the class.
What is scope of a private member
variable of a C# class?
Private access specifier allows a class to hide
its member variables and member functions from other functions and objects.
Only functions of the same class can access its private members. Even an
instance of a class cannot access its private members.
What is scope of a protected member
variable of a C# class?
Protected access specifier allows a child class
to access the member variables and member functions of its base class. This way
it helps in implementing inheritance.
What is scope of a Internal member
variable of a C# class?
Internal access specifier allows a class to
expose its member variables and member functions to other functions and objects
in the current assembly. In other words, any member with internal access
specifier can be accessed from any class or method defined within the application
in which the member is defined.
What is scope of a Protected
Internal member variable of a C# class?
The protected internal access specifier allows a
class to hide its member variables and member functions from other class
objects and functions, except a child class within the same application. This
is also used while implementing inheritance.
What are nullable types in C#?
C# provides a special data types, the nullable
types, to which you can assign normal range of values as well as null values.
For example, you can store any value from
-2,147,483,648 to 2,147,483,647 or null in a Nullable<Int32> variable.
Similarly, you can assign true, false, or null in a Nullable<bool>
variable.
What is the use of Null Coalescing
Operator (??) in C#?
The null coalescing operator is used with the
nullable value types and reference types. It is used for converting an operand
to the type of another nullable (or not) value type operand, where an implicit
conversion is possible.
If the value of the first operand is null, then
the operator returns the value of the second operand, otherwise it returns the
value of the first operand.
Can you create a function in C#
which can accept varying number of arguments?
By using the params keyword, a method parameter
can be specified which takes a variable number of arguments or even no
argument.
Can you pass additional type of
parameters after using params in function definition?
No! additional parameters are not permitted
after the params keyword in a method declaration. Only one params keyword is
allowed in a method declaration.
Which class acts as a base class for
all arrays in C#?
The Array class is the base class for all the
arrays in C#. It is defined in the System namespace. The Array class provides
various properties and methods to work with arrays.
How to sort an array in C#?
Using Array.sort(array) function. It sorts the
elements in an entire one-dimensional Array using the IComparable
implementation of each element of the Array.
How to sort an array in C# in
descending order?
First sort the array using Array.sort(array)
then reverse the same using Array.reverse(array) method.
What is a structure in C#?
In C#, a structure is a value type data type. It
helps you to make a single variable hold related data of various data types.
The struct keyword is used for creating a structure.
Structures are used to represent a record. To
define a structure, you must use the struct statement. The struct statement
defines a new data type, with more than one member for your program.
What are the differences between a
class and structure
Classes and Structures have the following basic
differences:
·
classes are reference
types and structs are value types.
·
structures do not
support inheritance.
·
structures cannot have
default constructor.
What is a enumeration in C#?
An enumeration is a set of named integer
constants. An enumerated type is declared using the enum keyword.
C# enumerations are value data type. In other
words, enumeration contains its own values and cannot inherit or cannot pass
inheritance.
What is the default access for a
class?
Default access specifier for a class type is
internal.
What is the default access for a
class member?
Default access for the members is private.
What is inheritance?
One of the most important concepts in
object-oriented programming is inheritance. Inheritance allows us to define a
class in terms of another class, which makes it easier to create and maintain
an application. This also provides an opportunity to reuse the code
functionality and speeds up implementation time.
When creating a class, instead of writing
completely new data members and member functions, the programmer can designate that
the new class should inherit the members of an existing class. This existing
class is called the base class, and the new class is referred to as the derived
class.
The idea of inheritance implements the IS-A
relationship. For example, mammal IS A animal, dog IS-A mammal hence dog IS-A
animal as well, and so on.
Is multiple inheritance supported in
C#?
No! C# does not support multiple inheritance.
How to inherit a class in C#?
A class can be derived from more than one class
or interface, which means that it can inherit data and functions from multiple
base classes or interfaces. The syntax used in C# for creating derived classes
is as follows:
<acess-specifier> class <base_class>
{
...
}
class <derived_class> :
<base_class>
{
...
}
What is polymorphism?
The word polymorphism means having many forms.
In object-oriented programming paradigm, polymorphism is often expressed as
'one interface, multiple functions'.
What is the difference between
static polymorphism and dynamic polymorphism?
Polymorphism can be static or dynamic. In static
polymorphism, the response to a function is determined at the compile time. In
dynamic polymorphism, it is decided at run-time.
How C# supports static polymorphism?
C# provides two techniques to implement static
polymorphism. They are:
·
Function overloading
·
Operator overloading
What is early binding?
The mechanism of linking a function with an
object during compile time is called early binding. It is also called static
binding.
What is function overloading?
You can have multiple definitions for the same
function name in the same scope. The definition of the function must differ
from each other by the types and/or the number of arguments in the argument
list. You cannot overload function declarations that differ only by return
type.
How C# supports dynamic
polymorphism?
Dynamic polymorphism is implemented by abstract
classes and virtual functions.
What is a sealed class in C#?
When a class is declared sealed, it cannot be
inherited.
How will you create sealed abstract
class in C#?
No! It can not be created as abstract classes
cannot be declared sealed.
What are virtual functions in C#?
When you have a function defined in a class that
you want to be implemented in an inherited class(es), you use virtual
functions. The virtual functions could be implemented differently in different
inherited class and the call to these functions will be decided at runtime.
Is operator overloading supported in
C#?
You can redefine or overload most of the
built-in operators available in C#. Thus a programmer can use operators with
user-defined types as well.
Overloaded operators are functions with special
names the keyword operator followed by the symbol for the operator being
defined. Similar to any other function, an overloaded operator has a return
type and a parameter list.
What is an interface?
n interface is defined as a syntactical contract
that all the classes inheriting the interface should follow. The interface
defines the 'what' part of the syntactical contract and the deriving classes define
the 'how' part of the syntactical contract.
Interfaces define properties, methods, and
events, which are the members of the interface. Interfaces contain only the
declaration of the members. It is the responsibility of the deriving class to
define the members. It often helps in providing a standard structure that the
deriving classes would follow.
What is a preprocessor directives in
C#?
The preprocessor directives give instruction to
the compiler to preprocess the information before actual compilation starts.
All preprocessor directives begin with #, and
only white-space characters may appear before a preprocessor directive on a
line. Preprocessor directives are not statements, so they do not end with a
semicolon (;).
What is the use of conditional preprocessor
directive in C#?
You can use the #if directive to create a
conditional directive. Conditional directives are useful for testing a symbol
or symbols to check if they evaluate to true. If they do evaluate to true, the
compiler evaluates all the code between the #if and the next directive.
Which class acts as a base class for
all exceptions in C#?
C# exceptions are represented by classes. The
exception classes in C# are mainly directly or indirectly derived from the
System.Exception class. Some of the exception classes derived from the
System.Exception class are the System.ApplicationException and
System.SystemException classes.
What is the difference between
System.ApplicationException class and System.SystemException class?
The System.ApplicationException class supports
exceptions generated by application programs. Hence the exceptions defined by
the programmers should derive from this class.
The System.SystemException class is the base
class for all predefined system exception.
