C# Interview Questions for beginners — Part 1

Ndamulelo Nemakhavhani

Mar 11, 2019·4 min read

In this article we cover some of the Language Basics questions in C#.

1. Explain the role of the Main method in C# scripts

• The main method is the entry point for any executable C# application.
• Since it is called when the program starts executing, it must be a static class member. i.e. It can be called without instantiating the startup class.

class Startup{// Main Methodstatic void Main(string[] args)   {Console.WriteLine($"Count of command line arguments: {args.Length}");   }}# Alternatively, return type can be an int or a Task

• “If the return type is an int, it enables the program to communicate status information to other programs or scripts that invoke the executable file”. e.g. returning 0 indicates successful execution.
• More info.

2. How is a C# statement different from an expression statement

• A statement represent a line or lines of code terminated by a semi-colon or a sequence of statements enclosed in curly braces {}.
• Basically a program is made up of a sequence of statements that perform a specific task. e.g.

int age;  # 1. Declarative statement
int age = 3 # 2. Assignment statement
....
doSomething()   # invocation statement
if( a > 4 ) { doSomething() }  # conditional statements
.......

• An expression is an assignment statement where the value of a variable is obtained by evaluating a result of an operation or calling a function.

...
public string Fullname = "Myname" + "Surname";  ....
int discount = calculateDiscount();  # function call calculates and returns discount value

• More info.

3. Can you give an example of a situation where you’d use a struct over a class?

• Struct(s) are typically used in cases where the represented data is not expected to change after initialization.
• In addition, if the required behavior is that of a value type, a struct is used.
• More info.

4. Which keyword do we use to declare anonymous types?

• Anonymous types are declared using the keyword var.

...
var item = "Asp is fun!";   # type inferred as string by compiler
var player = new { team = "FCB", name = "Lionel Messi" };# You can also create arrays of anonymous objects as follows
var myArr = new[] { new { phone = "apple", size = 4 }, new { phone = "huawei", size= 1 }};

• More info.

5. Discuss the difference between sealed & abstract classes

• A sealed class cannot be used as a base class. This means that no class can be derived from this class.
• This feature can be useful in implementing security features to avoid spoofing. Read more about this here.
• An abstract class cannot be instantiated and hence it can only be used as a base class.
• This is useful for encapsulating common behavior among different classes and it also facilitates code re-usability.
• More info.

6. What is the difference between members marked as virtual and those marked as abstract inside a base class?

• A class that derives from an abstract class must implement all methods marked as abstract in the base class.
• Virtual methods can be optionally overridden by a derived class if needed or the original method from the base class can be used.
• This is because abstract methods are not implemented in the base class, i.e. They are only declared. On the contrary, virtual methods are always implemented in the base class.
• More info.

7. What are access modifiers does C# support? Describe each of these briefly

• Public — Class members accessible to all classes in the assembly and all assemblies that reference this assembly.
• Private-Class members only accessible inside the class that contains these members.
• Protected-Class members ‘visible’ in the defining class as well as in derived classes.
• Private protected-Accessible from the same or derived class within the same assembly.
• Internal-Accessible from anywhere within the parent assembly.
• Protected internal- Class members ‘visible’ in the defining class as well as in derived classes in the same or other assemblies.
• More info.

8. What is the purpose of ref and out keywords?

• Ref is typically used to mark arguments passed to functions as reference types instead of value types.

....
int void double( ref int x) { return x * 2 };# Inside main
...
int x = 1 ; # local variable x
var result = double(ref x);
...
# local variable x now equals 2

• The out keyword does the same thing as ref, except that, the value does not need to be initialized before it is passed to the function call.
• More info.

9. What is the fundamental difference between reference reference and value types?

• A reference value type holds the address to the memory location to where the actual value is stored.
• A value type holds the actual value that is assigned to it.

10. Explain what a delegate is using a code example

• A delegate represents a C# type that represents a method with a specified signature.

...# This delegate references any function which takes in two arguments # and returns an intpublic delegate int MyDelType(int x, int y);# You can use a delegate as follows
int summer(int x, int y){return x+y};..
MyDelType add = summer;var sum = add(1,2);
Console.WriteLine($"The sum of {1} and {2} is {sum}");

• Thank you for reading, if you have any comments or suggestions please feel free to ping me on the comments section below.
• Watch out for part 2 of this series.