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

The correct answer is B: SortedDictionary. SortedDictionary provides O(log n) lookup and maintains sorted order during iteration. Alternatives are slower or require post-processing.

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

The correct answer is B: ConcurrentBag. ConcurrentBag and other Concurrent* collections from System.Collections.Concurrent are thread-safe for multi-threaded scenarios without explicit locking.

An e-commerce application needs to handle concurrent user requests efficiently. Which ASP.NET Core feature is most suitable?

The correct answer is A: Async/Await with Task-based operations. Async/Await enables non-blocking I/O operations, allowing ASP.NET Core to handle more concurrent requests efficiently.

What will be the output of: string s1 = "Hello"; string s2 = "Hello"; Console.WriteLine(s1 == s2);

The correct answer is A: true. In C#, the == operator for strings compares their values, not references. Since both s1 and s2 contain "Hello", the result is true. This is different from object references comparison.

Which access modifier allows a member to be accessed only within the same assembly?

The correct answer is B: internal. 'internal' access modifier restricts member access to the same assembly only. This is useful for creating assembly-wide internal APIs.

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C# Programming
OOP in C#

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100 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 100

Topics in C# Programming

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

Q.1 Easy OOP in C#

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 in C#?

A It will compile successfully and create an instance with default implementations

B Compiler error - cannot instantiate an abstract class

C Runtime error - abstract class cannot be instantiated at runtime

D It will compile but throw an error only if ProcessPayment() is called

Correct Answer: B. Compiler error - cannot instantiate an abstract class

EXPLANATION

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 implement required functionality.

Test

Q.2 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.3 Hard OOP in C#

In a healthcare system, Doctor is a derived class from Employee. If you want to ensure that Doctor's constructor calls Employee's constructor before executing, which approach is correct?

A Use the 'base' keyword in Doctor's constructor initialization list

B Manually call Employee's constructor inside Doctor's constructor body

C Use the 'this' keyword to call parent constructor

D This is automatic and requires no explicit code

Correct Answer: A. Use the 'base' keyword in Doctor's constructor initialization list

EXPLANATION

The 'base' keyword in the constructor initialization list ensures the parent class constructor is called before the derived class constructor body executes, maintaining proper initialization order.

Test

Q.4 Hard OOP in C#

Consider a scenario where class X implements interfaces IA and IB, and both interfaces have a method named Process(). How should X implement this?

A X must implement Process() twice with different names

B X can implement Process() once, satisfying both interfaces using explicit interface implementation if needed

C This will cause a compilation error and is not allowed

D X must choose which interface's Process() to implement

Correct Answer: B. X can implement Process() once, satisfying both interfaces using explicit interface implementation if needed

EXPLANATION

C# allows one implementation to satisfy multiple interfaces when they have the same method signature. Explicit interface implementation can be used if methods need different behaviors.

Test

Q.5 Easy OOP in C#

Which statement is TRUE about abstract methods in C#?

A Abstract methods must be implemented in the base class

B Abstract methods cannot have any body and must be implemented in derived classes

C Abstract methods are only for static classes

D Abstract methods can be private

Correct Answer: B. Abstract methods cannot have any body and must be implemented in derived classes

EXPLANATION

Abstract methods have no implementation in the abstract class and force derived classes to provide their own implementation. They cannot be private as they must be overridable.

Test

Q.6 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.

Test

Q.7 Medium OOP in C#

In a banking application, you need to create a base class that cannot be instantiated but defines common properties for SavingsAccount and CheckingAccount. Which should you use?

A sealed class

B interface

C abstract class

D static class

Correct Answer: C. abstract class

EXPLANATION

An abstract class is ideal when you want to provide common functionality and properties to derived classes while preventing direct instantiation. It can have both abstract and concrete members.

Test

Q.8 Medium OOP in C#

Which of the following correctly demonstrates composition in C#?

A class Car : Vehicle { }

B class Car { private Engine engine; }

C class Car : Vehicle, IVehicle { }

D abstract class Car { }

Correct Answer: B. class Car { private Engine engine; }

EXPLANATION

Composition is represented by having an object of one class as a member variable of another class, allowing code reuse through object containment rather than inheritance.

Test

Q.9 Medium OOP in C#

What will be the result of the following C# code?

class Animal { }
class Dog : Animal { }
Dog dog = new Animal(); // Line 1

A Code compiles and runs successfully

B Compilation error: Cannot convert type 'Animal' to 'Dog'

C Runtime error

D Code runs but throws InvalidCastException

Correct Answer: B. Compilation error: Cannot convert type 'Animal' to 'Dog'

EXPLANATION

You cannot assign a base class instance to a derived class reference without explicit casting. This violates type safety rules in C#.

Test

Q.10 Medium OOP in C#

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

A abstract

B virtual

C sealed

D static

Correct Answer: C. sealed

EXPLANATION

The 'sealed' keyword prevents a class from being used as a base class for inheritance, ensuring that derived classes cannot override the sealed class.

Test

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