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 centered 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, color, 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, color, 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 initialized.

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 behavior 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 utilized 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 specialized 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 specialized 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.