C#.NET Interview Questions and Answers

What is C#?

C# is the best language for writing Microsoft .NET applications. C# provides the rapid application development found in Visual Basic with the power of C++. Its syntax is similar to C++ syntax and meets 100% of the requirements of OOPs like the following:

  • Abstraction
  • Encapsulation
  • Polymorphism
  • Inheritance

What is an Object?

According to MSDN, "a class or struct definition is like a blueprint that specifies what the type can do. An object is basically a block of memory that has been allocated and configured according to the blueprint. A program may create many objects of the same class. Objects are also called instances, and they can be stored in either a named variable or in an array or collection. Client code is the code that uses these variables to call the methods and access the public properties of the object. In an object-oriented language such as C#, a typical program consists of multiple objects interacting dynamically".

Objects helps us to access the member of a class or struct either they can be fields, methods or properties, by using the dot. To know more about object read the following links:

What is Managed or Unmanaged Code?

Managed Code

“The code, which is developed in .NET framework is known as managed code. This code is directly executed by CLR with the help of managed code execution. Any language that is written in .NET Framework is managed code”.

Unmanaged Code

The code, which is developed outside .NET framework is known as unmanaged code.
“Applications that do not run under the control of the CLR are said to be unmanaged, and certain languages such as C++ can be used to write such applications, which, for example, access low - level functions of the operating system. Background compatibility with the code of VB, ASP and COM are examples of unmanaged code”.
Unmanaged code can be unmanaged source code and unmanaged compile code. Unmanaged code is executed with the help of wrapper classes.
Wrapper classes are of two types:

  • CCW (COM Callable Wrapper).
  • RCW (Runtime Callable Wrapper).
  • Managed code and unmanaged code in .NET

What is Boxing and Unboxing?

Boxing and Unboxing both are used for type conversion but have some difference:


Boxing is the process of converting a value type data type to the object or to any interface data type which is implemented by this value type. When the CLR boxes a value means when CLR is converting a value type to Object Type, it wraps the value inside a System.Object and stores it on the heap area in application domain.


public void Function1()
   int i = 111;
   object o  = i;


Unboxing is also a process which is used to extract the value type from the object or any implemented interface type. Boxing may be done implicitly, but unboxing have to be explicit by code.


public void Function1()
   int o = 111;
   object i  = (int)o;

The concept of boxing and unboxing underlines the C# unified view of the type system in which a value of any type can be treated as an object.

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

What is the difference between Interface and Abstract Class?

What is Enum in C#

  • An enumeration is a collection of constants. That means you can create your own set of named constants by using enumerations.
  • Each constant will have a name with an integer value.
  • Syntax for Enumeration Declaration:
  •  public enum enumname
       Constant1 = value1, Constant2 = value2, Constant3 = value3 
  • Syntax for usage
  •   enumname.constantname  

Can “this” be used within a static method?

We can't use this in static method because keyword 'this' returns a reference to the current instance of the class containing it. Static methods (or any static member) do not belong to a particular instance. They exist without creating an instance of the class and call with the name of a class not by instance so we can’t use this keyword in the body of static Methods, but in case of Extension Methods we can use it the functions parameters. Let’s have a look on “this” keyword.

The "this" keyword is a special type of reference variable that is implicitly defined within each constructor and non-static method as a first parameter of the type class in which it is defined. For example, consider the following class written in C#.

Define Property in C#.net?

Properties are members that provide a flexible mechanism to read, write or compute the values of private fields, in other words by the property we can access private fields. In other words we can say that a property is a return type function/method with one parameter or without a parameter. These are always public data members. It uses methods to access and assign values to private fields called accessors.

Now question is what are accessors?

The get and set portions or blocks of a property are called accessors. These are useful to restrict the accessibility of a property, the set accessor specifies that we can assign a value to a private field in a property and without the set accessor property it is like a read-only field. By the get accessor we can access the value of the private field, in other words it returns a single value. A Get accessor specifies that we can access the value of a field publically.

We have the three types of properties

  • Read/Write.
  • ReadOnly.
  • WriteOnly

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

What is IEnumerable<> in c#?

IEnumerable is the parent interface for all non-generic collections in System.Collections namespace like ArrayList, HastTable etc. that can be enumerated. For the generic version of this interface as IEnumerable which a parent interface of all generic collections class in System.Collections.Generic namespace like List<> and more.

In System.Collections.Generic.IEnumerable have only a single method which is GetEnumerator() that returns an IEnumerator. IEnumerator provides the power to iterate through the collection by exposing a Current property and Move Next and Reset methods, if we doesn’t have this interface as a parent so we can’t use iteration by foreach loop or can’t use that class object in our LINQ query.

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