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

The correct answer is B: HashSet. HashSet uses a hash table internally, providing O(1) average case lookup, insert, and delete operations.

Which of the following correctly demonstrates string interpolation in C# 6.0 and above?

The correct answer is C: string name = "John"; Console.WriteLine($"Hello {name}");. String interpolation uses the $ prefix with curly braces to embed expressions. Option C shows the correct syntax: $"Hello {name}". The @ symbol creates verbatim strings, not interpolated strings.

Which of the following correctly demonstrates the ternary operator in C#?

The correct answer is B: int x = (age >= 18) ? 1 : 0;. Option B is correct as both branches return int (1 or 0). Option A has type mismatch (string in int). Option C has wrong syntax. Option D has type mismatch.

An abstract class Shape has an abstract method CalculateArea(). Which statement is true?

The correct answer is B: Shape cannot be instantiated; derived classes must implement CalculateArea(). Abstract classes cannot be instantiated. Derived classes must provide concrete implementations of all abstract methods, enforcing a contract.

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C# Programming

C# and .NET for campus placement

60 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 60

Topics in C# Programming

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

Q.1 Hard Collections

In a high-concurrency distributed system, which collection from System.Collections.Concurrent is best for one-to-many relationships?

A ConcurrentDictionary

B ConcurrentBag

C ConcurrentDictionary

D BlockingCollection

Correct Answer: C. ConcurrentDictionary

EXPLANATION

For one-to-many relationships with concurrent access, combining ConcurrentDictionary with ConcurrentBag (or List) provides thread-safe multi-value storage per key.

Test

Q.2 Hard Collections

Which collection should be used when you need both indexed access and automatic sorting?

A List

B SortedSet

C SortedList (with integer keys as indices)

D Queue

Correct Answer: C. SortedList (with integer keys as indices)

EXPLANATION

SortedList<K,V> maintains sorted order by keys and allows O(1) index-based access. SortedSet<T> doesn't support indexing.

Test

Q.3 Hard Collections

In a real-time cache system with limited memory, which collection supports automatic eviction of least recently used items?

A Dictionary

B MemoryCache from System.Runtime.Caching

C ConcurrentDictionary

D LinkedHashMap

Correct Answer: B. MemoryCache from System.Runtime.Caching

EXPLANATION

MemoryCache provides LRU-style eviction and memory management policies. Basic collections don't have built-in LRU functionality.

Test

Q.4 Hard Collections

In a dictionary with 1000 items, what is the expected number of operations for TryGetValue() in C# 2024-25?

A 1 (O(1))

B 500 (O(n))

C 10 (O(log n))

D 1000 (O(n))

Correct Answer: A. 1 (O(1))

EXPLANATION

TryGetValue() uses hashing for lookup, providing O(1) average case complexity regardless of dictionary size.

Test

Q.5 Hard Collections

Which LINQ method combines multiple sequences into a single result with cartesian product?

A Union()

B SelectMany()

C Concat()

D Merge()

Correct Answer: B. SelectMany()

EXPLANATION

SelectMany() (also called flatMap in other languages) flattens nested sequences and creates a cartesian product of collections.

Test

Q.6 Hard Collections

In a real-time data processing application, which concurrent collection would be best for producer-consumer pattern?

A ConcurrentBag

B BlockingCollection

C ConcurrentQueue

D ConcurrentDictionary

Correct Answer: B. BlockingCollection

EXPLANATION

BlockingCollection<T> supports blocking operations for producer-consumer patterns, allowing threads to wait for items or space.

Test

Q.7 Hard Collections

In a competitive exam scenario, if you need both fast lookup and sorted iteration, which should you choose?

A List + Sort

B SortedDictionary

C HashSet

D Dictionary + LINQ

Correct Answer: B. SortedDictionary

EXPLANATION

SortedDictionary provides O(log n) lookup and maintains sorted order during iteration. Alternatives are slower or require post-processing.

Test

Q.8 Hard Collections

Which LINQ method should you use to get distinct elements from a List while maintaining performance?

A list.Where(x => !list.Skip(list.IndexOf(x)+1).Contains(x))

B list.Distinct()

C list.GroupBy(x => x).Select(g => g.First())

D new HashSet(list)

Correct Answer: B. list.Distinct()

EXPLANATION

Distinct() is the standard LINQ method for removing duplicates. While HashSet works, Distinct() is more idiomatic.

Test

Q.9 Hard Collections

What happens when you call Clear() on a Dictionary?

A Dictionary becomes null

B All key-value pairs are removed, capacity unchanged

C Dictionary capacity is reduced to 0

D An exception is thrown

Correct Answer: B. All key-value pairs are removed, capacity unchanged

EXPLANATION

Clear() removes all elements but doesn't deallocate capacity. The dictionary remains usable with count=0.

Test

Q.10 Hard Collections

Which collection type allows you to iterate in reverse order efficiently?

A Queue

B LinkedList

C Stack

D SortedSet

Correct Answer: B. LinkedList

EXPLANATION

LinkedList<T> has Reverse enumerator for efficient reverse iteration. Others don't have built-in reverse iteration support.

Test

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