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

The correct answer is B: Enum. Enum is a value type in C#. String, Interface, and Delegate are reference types.

Which keyword is used to prevent a class from being inherited in C#?

The correct answer is B: sealed. 'sealed' keyword prevents a class from being inherited in C#. 'final' is Java syntax. 'abstract' requires a class to be inherited. 'static' makes members class-level, not related to inheritance.

Consider a payment processing system where PaymentProcessor is an abstract class with an abstract method ProcessPayment(). CreditCardProcessor and UPIProcessor are derived classes. What will happen if you try to instantiate PaymentProcessor directly

The correct answer is B: Compiler error - cannot instantiate an abstract class. Abstract classes in C# cannot be instantiated directly. The compiler enforces this rule at compile-time. Abstract classes serve as blueprints and must be inherited by concrete classes that provide implementations for all abstract members. This ensures proper design and forces derived classes to impl

Which statement about anonymous functions in C# is TRUE?

The correct answer is B: Lambda expressions are a type of anonymous function. Lambda expressions (introduced in C# 3.0) are a concise form of anonymous functions. They can infer return types and parameter types, and can access outer scope variables.

Which of the following is a correct way to declare a property with auto-implementation in C#?

The correct answer is A: public int Age { get; set; }. Auto-implemented properties in C# use the syntax: public Type PropertyName { get; set; } without explicitly defining the backing field.

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C# Programming

C# and .NET for campus placement

154 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 154

Topics in C# Programming

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

Q.31 Medium Collections

Which collection should be used when you need sorted key-value pairs automatically?

A Dictionary

B SortedDictionary

C List

D Hashtable

Correct Answer: B. SortedDictionary

EXPLANATION

SortedDictionary<K,V> automatically maintains keys in sorted order. Dictionary<K,V> maintains insertion order but not sorted order.

Test

Q.32 Medium Collections

Consider: Dictionary dict = new(); dict.Add("a", 1); dict.Add("a", 2); What happens?

A Value is updated to 2

B ArgumentException is thrown

C Both values are stored

D The second add is ignored

Correct Answer: B. ArgumentException is thrown

EXPLANATION

Dictionary enforces unique keys. Attempting to add a duplicate key throws ArgumentException. Use dict["a"] = 2 to update.

Test

Q.33 Medium Collections

What is the difference between Stack.Push() and Stack.Pop()?

A Push adds, Pop removes and returns the element

B Pop adds, Push removes and returns the element

C Both are identical operations

D Push returns a value, Pop doesn't

Correct Answer: A. Push adds, Pop removes and returns the element

EXPLANATION

Push() adds an element to the stack, while Pop() removes and returns the top element. If stack is empty, Pop throws InvalidOperationException.

Test

Q.34 Medium Collections

Which interface must be implemented to use a collection in a foreach loop?

A IEnumerable

B ICollection

C IList

D IComparable

Correct Answer: A. IEnumerable

EXPLANATION

IEnumerable interface provides GetEnumerator() method, enabling foreach iteration. IEnumerable<T> is the generic version.

Test

Q.35 Medium Collections

What happens when you try to access an index beyond the Count in a List?

A Returns null

B Returns the last element

C Throws IndexOutOfRangeException

D Returns default value of type

Correct Answer: C. Throws IndexOutOfRangeException

EXPLANATION

Accessing an invalid index throws IndexOutOfRangeException. This is a runtime error that must be caught to prevent program crashes.

Test

Q.36 Medium Collections

Which collection maintains insertion order but uses a hash table for faster lookups?

A Dictionary

B SortedDictionary

C LinkedHashMap (not in C#)

D Both A and B

Correct Answer: A. Dictionary

EXPLANATION

Dictionary<K,V> in .NET maintains insertion order (in recent versions) and provides O(1) lookup. SortedDictionary maintains sorted order instead.

Test

Q.37 Medium Collections

What is the time complexity of accessing an element by index in a 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 direct index-based access in constant time O(1).

Test

Q.38 Medium Collections

Which method removes all elements from a collection in C#?

A Remove()

B RemoveAt()

C Clear()

D Delete()

Correct Answer: C. Clear()

EXPLANATION

Clear() removes all elements from a collection. Remove() removes a specific element, and RemoveAt() removes an element at a specific index.

Test

Q.39 Medium OOP 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?

A Encapsulation - using private fields with public properties to control access

B Inheritance - creating a base Product class with derived classes for each product type

C Polymorphism - overriding methods in derived classes to change behavior

D Abstraction - using abstract classes to hide implementation details

Correct Answer: A. Encapsulation - using private fields with public properties to control access

EXPLANATION

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 systems.

Test

Q.40 Medium OOP in C#

In a logistics system, both Truck and Bicycle need to calculate delivery cost. Instead of duplicating code, you decide to use an interface. What advantage does this provide?

A It enforces implementation of delivery cost calculation in both classes

B It automatically calculates delivery cost

C It restricts inheritance to one parent class only

D It provides default implementation for all methods

Correct Answer: A. It enforces implementation of delivery cost calculation in both classes

EXPLANATION

Interfaces establish a contract that forces implementing classes to provide their own logic for calculating delivery costs, promoting code consistency without duplicating implementation.

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