What are the 10 most common C# interview questions and how to answer them

From simple questions on the ad­vant­ages of C# to ex­plain­ing different elements of the pro­gram­ming language and how they can be used, we’ve created a list of the 10 most important questions for a C# job interview.

This article high­lights ten commonly asked questions in a job interview for a de­vel­op­ment position. We’ve also included answers to each of these questions. While these questions cover a range of topics from simple to detailed, there are lots of other potential questions about C# and its special features.

This article provides an initial overview of different questions that may be asked, ranging from straight­for­ward ones to ones that are more specific and ask for certain details. This article can also help you to un­der­stand how to prepare yourself for an interview that aims to test your knowledge of a specific pro­gram­ming language.

Question 1: What are special features of C# and what ad­vant­ages does the pro­gram­ming language offer?

With its special de­vel­op­ment en­vir­on­ment Visual Studio, C# is fun­da­ment­ally designed for speed. As an object-oriented pro­gram­ming language, C# also scores points with its simple and modern app de­vel­op­ment, which is both versatile and powerful. This is why many de­velopers opt for C# when deciding which pro­gram­ming language to learn.

C# is fun­da­ment­ally struc­tured around classes and objects, strongly adhering to typing prin­ciples. It provides func­tion­al­it­ies such as ab­strac­tion, en­cap­su­la­tion and in­her­it­ance. The pro­gram­ming language is primarily intended for de­vel­op­ment within the Microsoft .NET ecosystem.

Because of its alignment with the .NET framework, C# has its own structure where many types within .NET struc­tures inherit from the object class. As a result, these classes inherit methods, prop­er­ties, fields and events. This hier­arch­ic­al structure fa­cil­it­ates con­sist­ency and in­ter­op­er­ab­il­ity within the .NET ecosystem.

Question 2: What does the clas­si­fic­a­tion ‘object’ mean in C#?

Un­der­stand­ing objects in C# hinges on grasping the fun­da­ment­al prin­ciples of the language. At its core, C# is an object-oriented pro­gram­ming language, where classes serve as the found­a­tion. A class de­lin­eates the structure of data and dictates how it’s stored, managed and trans­ferred in C#. Es­sen­tially, it serves as the blueprint for all other data struc­tures.

Objects are real elements within C# that also occupy real values within the available memory. All entities that are equipped with very specific char­ac­ter­ist­ics or that perform a specific task within the software can be con­sidered objects. The object type is defined by a class, and class instances form the framework for their further structure.

For example, let’s say we’re designing a program centred around a tele­vi­sion. First, we need to define an entity as the starting point. In this case, we could create the class ‘Tele­vi­sion’. Within this class, we want to define five prop­er­ties: man­u­fac­turer, model, colour, size and price. These prop­er­ties are members of the class. Other members of the class could be events, methods or fields, all of which col­lect­ively make up an object.

To program a Sony Bravia as an instance of a TV, we can specify Sony, Bravia, Black, 50 and 500 as prop­er­ties when creating this object. This defines the in­form­a­tion on man­u­fac­turer, model, colour, size and price. The Sony tele­vi­sion is therefore an instance of the Tele­vi­sion class. To make this class ac­cess­ible, it’s important to define it as public and not as private or protected.

Question 3: What is the dif­fer­ence between managed and unmanaged code in C#?

Managed code

Managed code in C# is all code created using the .NET Framework. This type of code is executed directly by the Common Language Runtime (CLR). The CLR manages the life cycle of the code, including object creation, memory al­loc­a­tion and object disposal.

Unmanaged code

Code developed outside the .NET Framework is referred to as unmanaged code. This category en­com­passes all ap­plic­a­tions that are not executed under the control of the CLR.

The .NET Framework provides a function that can convert unmanaged code into managed code and vice versa. This cap­ab­il­ity is par­tic­u­larly useful as it fa­cil­it­ates the seamless in­teg­ra­tion of object creation and execution as well as code disposal within the framework.

Question 4: What is the dif­fer­ence between struct and class?

In C#, the terms class (class) and structure (struct) refer to user-defined data types. These data types have some fun­da­ment­al dif­fer­ences though.

Structure

• As a value type in C#, struc­tures always im­pli­citly inherit from System.ValueType.
• Struc­tures cannot be derived from other types.
• As a rule, a structure is used for smaller amounts of data.
• Struc­tures cannot be abstract and as such, require direct im­ple­ment­a­tion.
• It is not possible to assign a standard con­struct­or to a structure.
• Creating an object using the new keyword is not mandatory.

Class

• As a reference type in C#, classes always im­pli­citly inherit from System.Object.
• Classes can be derived from other classes, which enables in­her­it­ance.
• As a rule, a class is used for larger amounts of data or more complex struc­tures.
• Classes can be abstract, which means that they do not allow direct in­stan­ti­ation.
• In contrast to struc­tures, classes can have a standard con­struct­or if they need one.

Question 5: What is the dif­fer­ence between an interface and an abstract class in C#?

In­ter­faces (in­ter­faces) and abstract classes (abstract classes) both specify code contract classes, e.g., pre­con­di­tions or object in­vari­ants, for derived classes. Despite this com­mon­al­ity, there are many dif­fer­ences, as the func­tion­al­ity of in­ter­faces and abstract classes shows.

Code contract classes can be used to specify pre­con­di­tions, post­con­di­tions and object in­vari­ants. Pre­con­di­tions are re­quire­ments that must be fulfilled when entering a method or property.

In terms of in­her­it­ance, abstract classes can contain methods with im­ple­men­ted code in addition to abstract methods, while in­ter­faces require all methods to be abstract. Because of this, abstract classes need the abstract keyword for de­clar­a­tion.

Since C# doesn’t support multiple in­her­it­ance of classes, a class can’t inherit from more than one abstract class. However, several in­ter­faces can be im­ple­men­ted by a class in order to enable multiple in­her­it­ance of in­ter­faces.

An abstract class can have con­struct­ors that can be invoked by derived classes. In­ter­faces cannot contain con­struct­ors because they’re not instances and therefore cannot be ini­tial­ised.

Question 6: What are prop­er­ties in C#?

In C#, prop­er­ties are an element of a class that let you read, write or calculate the value of a privately declared field. Prop­er­ties can be used to access public in­ter­faces or allow changes to data stored in a class.

Prop­er­ties are a fun­da­ment­al aspect of object-oriented pro­gram­ming in C# and are commonly used in ap­plic­a­tions to provide clean and secure access to class data.

They are declared using the get and set accessors, which define the behaviour for reading or setting the property value. The get accessor retrieves the value of the property, while the set accessor sets the value of the property. A property can have one or both accessors. This depends on whether the property is (or should be) read-only or read/write.

Question 7: What is meant by boxing and unboxing in C#?

Boxing and unboxing are used in C# for type con­ver­sions.

• The con­ver­sion from a value type to a reference type is known as boxing. This could, for example, be con­vert­ing a simple data type like int to the data type object. Boxing is an implicit con­ver­sion.
• Con­vert­ing from a reference type to a value type, on the other hand, is called unboxing. Unboxing can only take place with the exact value type that was ori­gin­ally boxed, for example, con­vert­ing object back to int.

Question 8: What is enu­mer­a­tion(enum) and what is it used for in C#?

An enum is a value type with a set of related named constants. This group is also referred to as an ‘enu­mer­at­or list’. In C#, enums are enu­mer­ated data types that are primitive and user-defined. The keyword enum is used to declare an enu­mer­a­tion.

Enums in the .NET Framework are utilised for creating numeric constants. Each member of an enum is of the enum type, and a numerical value is needed for each enum type. These enum values are immutable. Enums can be rep­res­en­ted as character strings and ma­nip­u­lated as integers.

The default type of the enu­mer­a­tion element is int. By default, the first enu­mer­at­or has the value 0 and the value of each suc­cess­ive enu­mer­at­or is increased by 1. However, these values can also be set manually, for example 10 = On and 20 = Off.

Question 9: What is the dif­fer­ence between Dispose and Finalize in C#?

In C#, both methods are used to release resources.

The Dispose method releases unmanaged resources, such as database con­nec­tions that aren’t auto­mat­ic­ally managed by the .NET runtime host. It’s normally im­ple­men­ted in a class. This in turn im­ple­ments the ID­ispos­able interface, which defines the Dispose method.

This method is ex­pli­citly called by client code to release resources that are no longer needed. Al­tern­at­ively, it can be im­pli­citly invoked with the using statement, ensuring that the Dispose method is called when the object goes out of scope.

The Finalize method, on the other hand, is employed to carry out cleanup op­er­a­tions on an object just before the garbage col­lec­tion process occurs. As a result, it’s typically im­ple­men­ted in a class that overrides the Object.Finalize method.

Question 10: What are the ad­vant­ages of extension methods in C#?

Extension methods let de­velopers expand the func­tion­al­ity of an existing type without altering the original type or creating a new derived type. They allow for methods to be added to existing classes, struc­tures, in­ter­faces, enums, etc., even if the methods were not initially defined within the type.

Extension methods are declared within a static class and defined as static methods, featuring a unique first parameter named this. This parameter specifies the type being extended, enabling the extension method to be invoked as if it were an instance method of that type.

What kinds of questions can I expect in a C# interview?

Knowing who’s in­ter­view­ing you can provide you with more insight into the nature of the questions you will be asked. Re­cruit­ers sometimes lack the expertise required for in-depth dis­cus­sions on spe­cial­ised areas like cat­egor­ies or objects in C#. So, if the in­ter­view­er is a technical lead or a member of the de­vel­op­ment team, it’s more likely that the interview questions will delve into specific pro­gram­ming concepts and skills.

If the lead software architect or web developer is present, it’s likely that they’ll ask spe­cial­ised questions, es­pe­cially if you are applying for roles beyond entry level. This is because future col­leagues want to know how new team member will be able to assist them in their daily tasks.