Which of the following data types in C# is a value type?

The correct answer is B: int. int is a value type (primitive type). string, object, and arrays are reference types in C#.

In a real-time inventory management system, a Product class needs to track stock levels that should not be modified directly from outside the class. Which OOP principle should be applied here, and how?

The correct answer is A: Encapsulation - using private fields with public properties to control access. Encapsulation is the principle of bundling data and methods together while hiding internal details. Using private fields with public properties (getters/setters) allows controlled access to the stock level, preventing unauthorized direct modifications. This is the standard practice in inventory syst

What is the correct order of constructor execution in multilevel inheritance? class A { public A() { Console.WriteLine("A"); } } class B : A { public B() { Console.WriteLine("B"); } } class C : B { public C() { Console.WriteLine("C"); } } new C();

The correct answer is B: A B C. Constructor execution follows from parent to child. When C() is called, it implicitly calls B() which calls A(). So output is: A B C. Base class constructors execute before derived class constructors.

In C#, what is the correct way to implement explicit interface implementation?

The correct answer is B: private void InterfaceName.MethodName() { }. Explicit interface implementation is always private by convention and accessed through interface reference only, not through class instance directly.

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

The correct answer is B: Returns the top element without removing it. Peek() returns the top element without modifying the stack. Pop() removes and returns it. Peek() throws InvalidOperationException if the stack is empty.

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C# Programming

C# and .NET for campus placement

154 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 154

Topics in C# Programming

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

Q.1 Medium Collections

In a scenario with frequent additions and removals at both ends, which collection is most efficient?

A List

B LinkedList

C Queue

D Stack

Correct Answer: B. LinkedList

EXPLANATION

LinkedList<T> provides O(1) AddFirst(), AddLast(), RemoveFirst(), and RemoveLast() operations. List<T> requires O(n) for head removals due to reindexing.

Test

Q.2 Medium Collections

What is the time complexity of Contains() method in a HashSet?

A O(n)

B O(log n)

C O(1) average case

D O(n²)

Correct Answer: C. O(1) average case

EXPLANATION

HashSet<T> uses hash-based lookup for Contains(), achieving O(1) average-case time complexity, with O(n) worst-case in case of hash collisions.

Test

Q.3 Medium Collections

Which collection maintains elements in sorted order and is backed by a binary search tree?

A SortedList

B SortedDictionary

C SortedSet

D TreeMap

Correct Answer: B. SortedDictionary

EXPLANATION

SortedDictionary<K,V> uses a red-black tree (binary search tree) for O(log n) operations. SortedSet<T> also uses BST but for single values.

Test

Q.4 Medium Collections

In a data processing pipeline, if you need FIFO (First-In-First-Out) semantics with O(1) enqueue/dequeue, which collection is best?

A Stack

B LinkedList

C Queue

D SortedList

Correct Answer: C. Queue

EXPLANATION

Queue<T> provides FIFO semantics with O(1) Enqueue() and Dequeue() operations. Stack<T> is LIFO, and LinkedList operations vary.

Test

Q.5 Medium Collections

Which LINQ method is used to convert a Dictionary to a List of key-value pairs?

A ToArray()

B ToList()

C AsEnumerable()

D Cast()

Correct Answer: B. ToList()

EXPLANATION

ToList() converts the Dictionary's KeyValuePair<K,V> enumeration into a List<KeyValuePair<K,V>>. ToArray() would create an array instead.

Test

Q.6 Medium Collections

What happens when you modify a List while iterating over it using a foreach loop?

A It works without issues

B It throws InvalidOperationException

C It silently skips elements

D It doubles the iteration time

Correct Answer: B. It throws InvalidOperationException

EXPLANATION

Modifying a collection during enumeration invalidates the enumerator and throws InvalidOperationException. Use a for loop or ToList() to avoid this.

Test

Q.7 Medium Collections

In a multiprocessing environment, which thread-safe collection should be used for concurrent operations?

A List

B ConcurrentBag

C HashSet

D Dictionary

Correct Answer: B. ConcurrentBag

EXPLANATION

ConcurrentBag<T> and other Concurrent* collections from System.Collections.Concurrent are thread-safe for multi-threaded scenarios without explicit locking.

Test

Q.8 Medium Collections

What is the primary difference between ArrayList and List?

A ArrayList is faster

B List is type-safe and more performant

C ArrayList uses generics

D No difference in modern C#

Correct Answer: B. List is type-safe and more performant

EXPLANATION

List<T> is strongly-typed (type-safe) and eliminates boxing/unboxing overhead. ArrayList is non-generic and slower due to boxing of value types.

Test

Q.9 Medium Collections

Which method should be used to safely check and retrieve a value from a Dictionary without throwing an exception?

A Get()

B TryGetValue()

C ContainsKey() followed by indexer

D Retrieve()

Correct Answer: B. TryGetValue()

EXPLANATION

TryGetValue() is the safe method that returns a boolean indicating success and outputs the value without throwing KeyNotFoundException.

Test

Q.10 Medium Collections

In a scenario where you need to store key-value pairs with fast lookup times, which collection is optimal?

A List

B Dictionary

C Queue

D LinkedList

Correct Answer: B. Dictionary

EXPLANATION

Dictionary<K,V> provides O(1) average-case lookup time using hash tables, making it optimal for key-value pair storage with fast retrieval.

Test

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