In C# 11, which feature enables you to define constraints on generic type parameters at compile-time?

The correct answer is A: Generic constraints with 'where' keyword. 'where' clause in generic types constrains type parameters (e.g., where T : class, where T : IComparable). C# 11 added 'allows ref struct' constraint.

In C#, what is the default access modifier for class members?

The correct answer is B: private. The default access modifier for class members in C# is 'private', which restricts access to within the class only.

Consider a BankAccount class with private balance field. How should external classes access this field safely?

The correct answer is B: Use public properties with get/set accessors. Properties with accessors (get/set) follow encapsulation principles, allowing controlled access while maintaining data validation logic within the property.

What is the primary purpose of encapsulation in OOP?

The correct answer is B: To hide internal implementation details and control access to data. Encapsulation bundles data and methods together, hiding internal implementation and controlling access through public interfaces, improving maintainability and security.

In C#, which keyword is used to create a constant variable that cannot be modified after initialization?

The correct answer is A: const. The 'const' keyword creates a compile-time constant in C#. 'readonly' creates a runtime constant, 'static' defines class-level members, and 'immutable' is not a C# keyword.

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Collections

C# and .NET for campus placement

15 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–15 of 15

Topics in C# Programming

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

Q.11 Hard Collections

In a concurrent environment, which collection should be used instead of Dictionary in C# 2024-25?

A Hashtable

B ConcurrentDictionary

C SortedDictionary

D List

Correct Answer: B. ConcurrentDictionary

EXPLANATION

ConcurrentDictionary<K,V> from System.Collections.Concurrent is thread-safe for multi-threaded applications, unlike Dictionary<K,V>.

Test

Q.12 Hard Collections

What is the difference between ICollection and IEnumerable in terms of capabilities?

A ICollection adds Count and Add/Remove/Clear methods

B Both are identical

C IEnumerable is a collection, ICollection is not

D ICollection cannot iterate, IEnumerable can

Correct Answer: A. ICollection adds Count and Add/Remove/Clear methods

EXPLANATION

IEnumerable<T> only provides iteration. ICollection<T> extends it with Count property and methods like Add(), Remove(), Clear() for modification.

Test

Q.13 Hard Collections

Consider: var result = list.OrderByDescending(x => x.Age).ThenBy(x => x.Name); What does this do?

A Sorts by Age ascending then Name descending

B Sorts by Age descending then Name ascending

C Sorts by Name then Age

D Throws a compilation error

Correct Answer: B. Sorts by Age descending then Name ascending

EXPLANATION

OrderByDescending sorts by Age in descending order. ThenBy applies secondary sort by Name in ascending order. This is a multi-level LINQ sort.

Test

Q.14 Hard Collections

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

A O(n)

B O(log n)

C O(1)

D O(n²)

Correct Answer: A. O(n)

EXPLANATION

HashSet<T> requires O(n) space to store n unique elements. Hash tables require linear space proportional to the number of stored elements.

Test

Q.15 Hard Collections

In C# 2024-25, which LINQ method would you use to find all elements matching a condition in a List?

A FindAll()

B Where()

C Both A and B work

D Filter()

Correct Answer: C. Both A and B work

EXPLANATION

Both FindAll() and Where() (LINQ) can filter collections. Where() returns IEnumerable and is more modern. FindAll() returns a List directly.

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