Which of the following correctly demonstrates nullable type syntax in C#?

The correct answer is A: int? x = null;. The correct syntax for nullable types is 'type?' where ? makes the value type nullable, allowing null values.

Which of the following demonstrates proper use of string interpolation in C# 6.0+?

The correct answer is A: $"Name is {name}". String interpolation uses the $ prefix followed by curly braces containing expressions.

What is covariance in C# generics and interfaces?

The correct answer is B: Allowing derived types where base types are expected in return types. Covariance (using 'out' keyword) allows a more derived type to be returned where a base type is expected, improving type safety and flexibility.

Which keyword is used to create a derived class in C#?

The correct answer is C: :. In C#, the colon (:) is used to indicate inheritance. For example, 'class Child : Parent' creates a derived class.

Which of the following correctly demonstrates an abstract class with an abstract method in C#?

The correct answer is A: public abstract class Base { public abstract void Method(); }. An abstract class uses the 'abstract' keyword, and abstract methods must be declared without implementation inside abstract classes.

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C# and .NET for campus placement

76 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 76

Topics in C# Programming

All Basics & Syntax 100 OOP in C# 100 Collections 71 ASP.NET Basics 19

Q.1 Easy Collections

What does the Peek() method do in a Stack?

A Removes and returns the top element

B Returns the top element without removing it

C Returns the bottom element

D Throws an exception if stack is empty

Correct Answer: B. Returns the top element without removing it

EXPLANATION

Peek() returns the top element without modifying the stack. Pop() removes and returns it. Peek() throws InvalidOperationException if the stack is empty.

Test

Q.2 Easy Collections

What is the space complexity of a HashSet with n elements?

A O(log n)

B O(n)

C O(n²)

D O(1)

Correct Answer: B. O(n)

EXPLANATION

HashSet<T> requires O(n) space to store n unique elements in the underlying hash table structure.

Test

Q.3 Easy Collections

What does the Add() method return when adding a duplicate element to a HashSet?

A true

B false

C throws an exception

D returns the index

Correct Answer: B. false

EXPLANATION

HashSet<T>.Add() returns false if the element already exists, true if added successfully. No exception is thrown.

Test

Q.4 Easy Collections

Which collection type uses a hash table internally and provides O(1) average lookup?

A TreeSet

B HashSet

C SortedSet

D LinkedHashSet

Correct Answer: B. HashSet

EXPLANATION

HashSet<T> uses a hash table internally, providing O(1) average case lookup, insert, and delete operations.

Test

Q.5 Easy Collections

Which method in Queue allows you to examine the front element without removing it?

A Peek()

B Front()

C Top()

D View()

Correct Answer: A. Peek()

EXPLANATION

Peek() returns the element at the front of the queue without removing it. Dequeue() would remove it.

Test

Q.6 Easy Collections

Which LINQ method should you use to transform each element of a collection into a new form?

A Transform()

B Select()

C Map()

D Convert()

Correct Answer: B. Select()

EXPLANATION

Select() is the LINQ method that projects each element to a new form, similar to map in functional programming languages.

Test

Q.7 Easy Collections

In a HashSet, what happens when you try to add a duplicate element?

A Throws InvalidOperationException

B Returns false and element is not added

C Replaces the existing element

D Adds the element creating duplicates

Correct Answer: B. Returns false and element is not added

EXPLANATION

HashSet<T>.Add() returns false if the element already exists and does not add duplicates, maintaining set semantics.

Test

Q.8 Easy Collections

Which IEnumerable method should be used to filter elements based on a condition and maintain type safety?

A Where

B Select

C Filter

D Find

Correct Answer: A. Where

EXPLANATION

Where<T> is a LINQ method that filters elements based on a predicate condition while maintaining type safety in the collection.

Test

Q.9 Easy Collections

Which method in Stack returns the top element without removing it?

A Pop()

B Peek()

C Top()

D Get()

Correct Answer: B. Peek()

EXPLANATION

Peek() returns the top element without removal. Pop() removes it. Top() and Get() are not Stack<T> methods.

Test

Q.10 Easy Collections

What is the time complexity of accessing an element by index in List?

A O(n)

B O(log n)

C O(1)

D O(n log n)

Correct Answer: C. O(1)

EXPLANATION

List<T> is backed by an array, allowing O(1) random access by index.

Test

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