Interview Q&A

• Interview questions are important for evaluating a candidate's proficiency in the C# programming language and assessing their coding and problem-solving skills.

Interview QnA

Here are some tricky interview questions in C# that can help you prepare for technical interviews:

1. 1 • What is C#?

⤏ C# (pronounced as "C sharp") is a high-level, object-oriented programming language developed by Microsoft within its .NET framework. It was created by Anders Hejlsberg and his team during the late 1990s as part of Microsoft's effort to provide a modern programming language that could simplify development across various platforms and devices.

1. 2 • the difference between '==' and '.Equals()' in C#:

⤏ The '==' operator compares the object references for equality, while '.Equals()' compares the contents of the objects. However, this behavior can be overridden by classes.

1. 3 • Differences between 'String' and 'StringBuilder' in C#:

⤏ In C#, 'String' is immutable, meaning once it's created, it cannot be changed, on the other hand, 'StringBuilder' is mutable and allows for efficient string manipulation.

1. 4 • What is the purpose of the 'using' statement in C#?

⤏ The 'using' statement in C# is primarily used for automatically disposing of unmanaged resources like database connections, file handles, etc., when they are no longer needed.

1. 5 • What is boxing and unboxing in C#?

⤏ Boxing is the process of converting a value type to the type object or to any interface type implemented by this value type. On the other hand, unboxing extracts the value type from the object.

1. 6 • The difference between 'throw' and 'throw ex' in C#:

⤏ 'throw ex' resets the stack trace, potentially hiding the original source of the exception, while 'throw' preserves the original stack trace.

1. 7 • difference between 'IEnumerable' and 'IEnumerator' in C#:

⤏ 'IEnumerable' provides an iterator over a collection, while 'IEnumerator' is responsible for managing the iteration state, allowing you to move through the collection and retrieve elements.

1. 8 • How does garbage collection work in C#?

⤏ Garbage collection in C# automatically reclaims memory that is no longer in use by the application. It tracks objects that are no longer referenced and frees up their memory, ensuring efficient memory management without manual intervention.

1. 9 • A function in C# to find the intersection of two arrays:

int[] Itrs(int[] nums1, int[] nums2) => nums1.Intersect(nums2).ToArray();

⤏ Use LINQ's 'Intersect' method to find the common elements between the two arrays and then converts the result into an array using 'ToArray()' method before returning it.

1. 10 • Implement a function in C# to check if a string is a palindrome.

bool IsPalindrome(string str) => str.SequenceEqual(str.Reverse());

⤏ Reverse the 'str' using 'Reverse()' method, and if they are equal, it returns 'true', indicating that the string is a palindrome; otherwise, it returns 'false'.

1. 11 • How does the 'lock' statement work in C#?

⤏ The 'lock' statement is used to ensure that a block of code runs only one thread at a time, preventing multiple threads from accessing shared resources concurrently.

1. 12 • Find the output of the following code below:

int number = 10;
int sum = number.ToString().Sum(c => c - '0');
Console.WriteLine(sum);

⤏ Output: 1

1. 13 • Find the output of the following code below:

int number = 5;
int cal = Enumerable.Range(1, number).Aggregate((x, y) => x * y);
Console.WriteLine(cal);

⤏ Output: 120

1. 14 • What is a nullable type in C#?

⤏ A nullable type allows variables to have the value of 'null' in addition to their normal range of values and they are declared by appending '?' to the underlying value type.

1. 15 • Difference between 'ref' and 'out' parameters in C#?

⤏ The 'ref' parameters must be initialized before passing them to the method, whereas 'out' parameters do not need to be initialized before being passed.

1. 16 • Find The second largest element in the array:

int[] array = [5, 10, 3, 8, 12]; 
int num = array.OrderByDescending(x => x).Skip(1).First();
Console.WriteLine(num);

⤏ Output: 10

1. 17 • What is a lambda expression in C#?

⤏ Lambda expressions are anonymous functions that allow you to write inline code instead of a separate method and they are often used in LINQ queries and asynchronous programming.

1. 18 • Difference between 'Task' and 'Thread' in C#:

⤏ 'Thread' represents an operating system thread, while 'Task' represents a unit of work that can be scheduled by the .NET Task Parallel Library. Tasks are more lightweight and provide higher-level abstractions for asynchronous programming.

1. 19 • Purpose of the 'as' and 'is' operators in C#?

⤏ The 'as' operator is used for explicit type conversion, returning null if the conversion fails. On the other hand, the 'is' operator is used for type testing, returning true if an object is of a specified type.

1. 20 • What is covariance and contravariance in C#?

⤏ Covariance allows for the assignment of a more derived type to a less derived type, while contravariance allows for the assignment of a less derived type to a more derived type.