Top 20 C# interview questions to review the essentials

Given today's competitive job market, proficiency in C# can set you apart — whether you're a developer or a hiring manager. C# is part of the .NET Framework, a general-purpose and object-oriented programming language. Designed for the Common Language Infrastructure (CLI), it offers a rich standard library and supports various high-level languages across multiple platforms.

What makes C# the go-to language for .NET development? Here are some reasons:

• Windows integration

• Automatic garbage collection

• Lambda expressions

• LINQ

C# has high scalability, fast development time, and a relatively gentle learning curve — it's no wonder C# is prominent in the tech sphere. If you're preparing for a .NET interview, it's a given that C# questions will be a significant part of the process. Companies are constantly searching for top-tier talent, and understanding the intricacies of C# is imperative. We've curated a list of common C# interview questions to help you review the essentials and navigate the specifics of your upcoming interview.

Top 20 C# coding interview questions#

1. What is C#? What is C# used for?#

C# is a contemporary, object-oriented programming language designed for type safety. It allows developers to construct a broad spectrum of secure and resilient applications within the .NET framework. The syntax and structure of C# are similar to C, C++, Java, and Javascript. Like other versatile programming languages, C# serves many development needs. Whether you're looking to build mobile or desktop applications, cloud services, websites, enterprise-grade software, or even games, you can do it all with C#.

2. What is an object in C#?#

In C#, an object is a block of memory allocated based on a class, which serves as a blueprint. Classes define the data structure, fields, and methods, while objects are real-world instances of these classes. For instance, if you have a class named "Table" with properties like Type, Color, and Size, an object can be a specific table, such as an "Ikea" table with its own set of these properties. Objects store actual values in computer memory and can exist in multiple instances, like different brands of tables.

3. What is method overloading?#

Method overloading in C# is a type of polymorphism that allows multiple methods with the same name but different signatures within a class. The compiler uses overload resolution to identify the correct method to invoke based on argument types and quantity.

4. What is managed and unmanaged code in C#?#

Managed code is written in .NET languages like C# and is executed and managed by the Common Language Runtime (CLR), which handles aspects like memory allocation. On the other hand, unmanaged code is written outside the .NET framework, such as in C or C++, and requires programmers to manage its lifecycle directly. The .NET framework enables interaction between the two using wrapper classes.

5. What are the different types of comments in C#?#

There are three different types of comments in C#:

• Single Line Comments ( // ):
  //Single line comment looks like this

• Multi-Line Comments ( /* */ ):
  /*Multiple line comment looks like this
  This is line 2
  Last line*/

• XML Comments ( /// ):
  /// This is an XML comment;
  /// Another line
  /// Third line 

6. Define boxing and unboxing in C##

Boxing in C# converts a value type into an object type, wrapping it in a System. Object and storing it on the managed heap. Unboxing is the opposite of this process. It extracts the original value type from the object. While boxing can be implicit, unboxing requires explicit code. Both processes highlight C #'s unified type system, allowing value types to be treated as objects.

7. What are circular references in C#?#

A circular reference is a situation that occurs when interdependent resources create a lock condition, making the resource inoperable. To manage circular references in C#, employ garbage collection; it identifies and collects these references.

8. What does partial class mean in C#?#

In C#, a partial class is a unique feature for splitting a class definition either within the same source code file or across multiple files. When instantiated, the class grants access to methods from all source files as part of a single object.

Partial classes must reside in the same namespace. Creating a partial class in different namespaces isn't feasible. The 'partial' keyword is used consistently to associate classes under the same class name within the same namespace.

9. What are jagged arrays?#

A jagged array is a multidimensional array in which each element is an array that can have different dimensions and sizes. It’s often referred to as an “array of arrays,” as it allows for varying row lengths.

10. What is a constructor in C#?#

A constructor is a specialized class method automatically called when a new class instance is created. Similar to methods, it contains instructions executed during object creation.

11. What is the method of inheriting a class into another class?#

In C#, the class that inherits from another class is called a 'derived class.' The parent class is referred to as the 'base class.' To create this relationship, a colon is used between these two classes: public class DerivedClass : BaseClass

12. What is abstract class and interface in C#?#

The key distinctions between an interface and an abstract class in C# are as follows:

• Interfaces enable multiple inheritance, unlike abstract classes.

• Abstract classes can contain abstract and concrete methods, while interfaces only have abstract methods.

• Abstract classes can declare and utilize variables, which is impossible in interfaces.

• All members in an abstract class are private by default, while in an interface, they're public. This can't be manually modified.

• The keyword 'abstract' is necessary to declare abstract methods in an abstract class, but this is not required in an interface.

• While abstract classes can have constructors, interfaces do not offer this feature.

13. Why do we use delegates in C#?#

Delegates perform the same way as function pointers in C++. They allow for the passing of methods as parameters and are commonly used for defining callback methods. They can also chain multiple methods, allowing several methods to be called through a single event. The use of delegates is essential for crafting more generic and type-safe functions.

14. What is 'this' in C#?#

In C#, the 'this' keyword is an implicitly defined reference variable in each constructor and non-static method. It serves as the first parameter and is of the class type in which it's defined. It's used to point to the current instance of the class and can also act as a modifier for the first parameter in an extension method.

15. Define value and reference types.#

Value and reference types store data differently. Value-type variables contain data in their memory space, while reference-type variables contain the object's address, where the data is stored. It points to the memory location.

16. What is serializable in C#?#

In C#, serialization converts an object into a byte stream for easy storage or transmission. This is an important process when transporting an object through a network. Deserialization reverses this, reading the object back from the byte stream.

17. What is the difference between an Array and an ArrayList?#

In C#, it’s crucial to know that Arrays are fixed-size and type-specific, while ArrayLists are dynamic and can hold multiple data types. Both are collections of elements, but arrays are much faster as they are a part of the language's core.

18. What does partial class mean in C#?#

A partial class (or struct) can have a partial method in C#. The method’s signature is in one part, and its implementation can be in the same or another part. So the definition of a partial class is present in two or more files. During compilation, these files merge back into one class. If there's no implementation, the method and its calls get removed during compilation.

19. How are static, public, and void different?#

'Public' variables are accessible throughout the application. 'Static' variables can be accessed globally without instantiating the class, but their global reach depends on the access modifier used. 'Void' indicates that a method returns no value.

20. Describe the differences between ref and out.#

'Ref' is used when a method needs to update a passed parameter. It passes arguments by reference, so changes in the method affect the original variable. 'Out' is used for methods that need to update multiple parameters.

Start Your C# Interview Prep Now#

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