Top 100 C# interview questions and answers 2024

6) List some of the advantages of C#?
Following are the advantages of C#

Easy to learn
Object-oriented
Component oriented
Part of the .NET framework

7) What are IDEs provided by Microsoft for C# development?

Following are the IDE’s used for C# development

Visual Studio Express (VCE)
Visual Studio (VS)
Visual Web Developer

8) What is the difference between a struct and a class in C#?

Struct & Class both are the user-defined data types but have some major differences:

9) What are the similarities between a struct and a class in C#?

Both can have a constructor, method/functions, properties, fields, constants, enumeration, events & event handler.
Structure & classes can implement the interface.
Both of them can have a constructor with & without parameters.
Both can have delegates & events.

10) What is oops and what are the different properties provided by oops?

Oops stands for object-oriented programming system. It is a problem-solving technique to think of real-world problems in terms of objects.

The following are different properties provided by Oops

Inheritance: It is a process of forming a new class from the existing class.
Example: A scientific calculator is an extended form of a calculator. Here, the calculator is the parent & scientific calculator is the child object.

Polymorphism: The ability to use an operator or functions in different ways giving different meanings to the function to the operator is called polymorphism.
Example: A person is behaving like a Child, professor, student, and then as a clerk. This is the power of polymorphism, a single object behaves in different forms.

Encapsulation: Encapsulate means to hide also called as data hiding. Encapsulation is used to hide the code & data in a single unit. It is a process of hiding all the internal details of an object from the outside world.
Example: Capsule: Capsule which hides medicine inside it.

Abstraction: Abstraction means showing only necessary information & hiding unnecessary information from the user. Abstraction let you focus on what object does instead of how it does it.

Example: Suppose you have a car, and u are riding car, now when you apply break you know that car is going to stop but you don’t know what is the process happened when you applied break. Abstraction means putting all the variables and methods in a necessary class.

11) The Differences between Abstraction and Encapsulation in C#?

#	Abstraction	Encapsulation
1.	Abstraction solves the problem at design level.	Encapsulation solves the problem at the implementation level.
2.	Abstraction is set to focus on the object instead of how it does it.	Encapsulation means hiding the internal details or mechanics of how an object does something.
3.	Abstraction is used for hiding the unwanted data and giving only relevant data.	Encapsulation is hiding the code and data into a single unit to protect the data from the outer world.
4.	Abstraction is implemented using interface & abstract class.	Encapsulation is implemented using private & protected access modifiers.
5.	Abstraction is outer layout in terms of design.	Encapsulation is inner layout in terms of implementation.
e.g.	Outer Look of an iPhone, like it has a display screen.	Inner Implementation detail of an iPhone, how Display Screen are connected with each other using circuits.

12) Explain sealed class in C#?

The sealed class is used to stop the class from being inherited from other classes. If you define a class in C# as “Sealed” & “nonheritable” in VB.NET, then you can not inherit the class further.

13) What are value types in C#?

Value types directly contain data and derived from System.ValueType.
Value types use the stack to store value.
Example: int, float, char, Bool, short

14) What are reference types in C#?

reference types stored the address of memory where data is stored
reference types use the heap to store value.
Example: Class, Interface, String, Object, Delegate, Array

15) What is the difference between value types and reference types?

#	Struct	Class
1.	They are stored on stack.	They are stored on heap.
2.	Memory is allocated at compile time.	Memory is allocated at runtime.
3.	The value type is popped on its own from the stack when they go out of scope.	Required garbage collector to free memory.
4.	Value type contains actual value.	Reference type contains reference to a value.
5.	Cannot contain null values. However, this can be achieved by nullable types.	Can contain null values.
e.g.	int, float, char, Bool, short.	Class, Interface, String, Object, Delegate, Array.

16) How do you get the size of value type?

using SizeOf operator.
Example: Console.WriteLine(“The size of long is {0}.”, sizeof(long));
output: The size of long is 8.

17) What are different types of the parameter in c#?

Following are different types of parameter in c#
1. Value parameter(in)
2. Reference parameter (ref)
3. Output parameter(out)
4. Parameter Array(param)

18) What is the difference between “out” and “ref” parameters in C#?

“out” parameter can be passed to a method and it need not be initialized where as “ref” parameter has to be initialized before it is used.

19) 18. List out the differences between Array and ArrayList in C#?
Array
1. Arrays are strongly typed collection of same datatype and these arrays are fixed length that cannot be changed during runtime.
2. Arrays belong to System.Array namespace.

ArrayList
1. Array lists are not strongly type collection. It will store values of different datatypes or same datatype. Array list size will increase or decrease dynamically it can take any size of values from any data type.
2. Arraylist belongs to System.Collection namespaces

20) Why we use keyword “const” in C#.

“Const” keyword is used for making an entity constant.

Example: const string _name = “techstudy”; Once we define a variable as a const then we can’t reassign the value of that variable(string _name).

21) What are Access Modifiers in C#?

Access Modifiers are basically used to control the accessibility of types and members with in the types. In C# there are 5 different types of Access Modifiers.

1. Public: Public is the most common access specifier in C#. It can be accessed from anywhere, that means there is no restriction on accessibility. It is accessible to all classes & projects.

2. Private: The range of the accessibility is limited only within the classes or struct in which they are declared.

3. Protected: All members in the current class & in derived classes can access the variables.

4. Internal: The type or member can be accessed by any code in the same assembly, but not from another assembly.

5. Protected Internal: The protected internal access specifier allows a class to hide its member functions & member variables from other class objects and functions, except a child class within the same application. This is also used while implementing inheritance.

 

22) How is the exception handling done in C#?

In C# there is a “try…catch & finally” block to handle the error.

try {
   // statements causing exception
} catch( ExceptionName e1 ) {
   // error handling code
}  finally {
   // statements to be executed
}

23) Can we execute multiple catch blocks in C#?

No. Once any exception has occurred it executes specific exception catch block and the control comes out.

24) What is Jagged Array in C#?

You can initialize a jagged array as

int[][] marks = new int[2][]{new int[]{12,13,52},new int[]{56,85,45,89}};

Where, marks is an array of two arrays of integers – marks[0] is an array of 3 integers and marks[1] is an array of 4 integers.

25) 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.

26) How to sort an array in C#?

Using Array.sort(array) function.

27) Is multiple inheritance supported in C#?

No! C# does not support multiple inheritance.

28) What is the difference between while, do while and for loop?

1) While loop checks for the condition first so it may not even enter into the loop if the condition is false.
2) do while loop executes the content of the loop once before checking the condition of the while.
3) For loop is similar to while loop except, the initialization of variable, condition check & increment happens at one place.

29) What is the difference between “constant” and “readonly” variables in C#?

“Const” keyword is used for making an entity constant. We cannot modify the value later in the code. Value assigning is always mandatory to constant variables.
“readonly” variable value can be changed during runtime and value to readonly variables can be assigned in the constructor or at the time of declaration.

30) What is the difference between dispose and finalize methods in c#?

Dispose: This method uses interface – “IDisposable” interface & it will free up both managed and unmanaged codes like – database connection, files etc. It belongs to the IDisposable interface. Implement this method when you are writing a custom class that will be used by other users.

Finalize: This method is called internally unlike Dispose method which is called explicitly. It is called by the garbage collector and can’t be called from the code. Finalize belongs to System.Object class. Implement this method when you have unmanaged resources in your code, and make sure that these resources are freed when the Garbage collection happens.

31) What is the difference between string and StringBuilder in c#?

String
The string is immutable. Immutable means once we create string object we cannot modify. Any operation like insert, replace or append happened to change string simply it will discard the old value and it will create a new instance in memory to hold the new value.
String belongs to System namespace

=>Example
string str = “hi”;
//It creates a new string instance instead of changing the old one
str += “help”;
str += “test”;

StringBuilder
String builder is mutable. Mutable means once we create string builder object we can perform any operation like insert, replace or append without creating new instance for every time.
StringBuilder belongs to System.Text namespace

=> Example
StringBuilder sb = new StringBuilder(“”);
//It does not creats new instance for every time.
sb.Append(“hi”);
sb.Append(“help “);
string str = sb.ToString();

32) List out some of the exceptions in C#?

Below are some of the exceptions in C#-
1. ArgumentNullException
2. NullReferenceException
3. IndexOutOfRangeException
4. DivideByZeroException
5. StackOverflowException
6. InvalidOperationException etc.

33) What do you mean by the delegate in C#?

Delegates are type safe pointers, unlike function pointers as in C++. A delegate is used to represent the reference to the methods of some return type and parameters.
Delegates are required because they can be used to write much more generic type safe functions.

34) What are the types of delegates in C#?

Following are the types of delegates in C# –
1. Single Delegate
2. Multicast Delegate
3. Generic Delegate
35) What is a multicast delegate?
A delegate having multiple handlers assigned to it is called multicast delegate. Each handler is assigned to a method.

36) What is Nullable Type in C#?

Variable types do not hold null values so to hold the null values we have to use nullable types. nullable types can have values either null or other values as well.
Eg: int? nullvariable = null;

37) What do you mean by boxing and unboxing in C#?

Boxing: This is the process of converting from value type to reference type.

Example
int i = 67; // i is a value type
object o = i; // i is boxed
System.Console.WriteLine(i.ToString()); // i is boxed

UnBoxing: It’s the process of converting reference type to value type.
System.Collections.ArrayList list = new System.Collections.ArrayList(); // list is a reference type
int n = 67; // n is a value type
list.Add(n); // n is boxed
n = (int)list[0]; // list[0] is unboxed

38) Can “this” be used 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.

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39) Explain is an interface class?

Interface class is an abstract class which has only public abstract methods & the methods only have the declaration and not the definition. These abstract methods must be implemented in the inherited classes.

40) Explain Abstract class?

We create an abstract class when we define a template that needs to be followed by all the derived classes. Abstract class can have implementation which should be implemented in the child class.

public class Student
{
 public Student() 
 { }
 public Student(String fullname) 
 { }
}

public int this[int index]

Public sealed class Singleton
{
Private static readonly Singleton _instance = new Singleton();
}

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