MCQs on Object-Oriented Programming (OOP) Basics | C#

Learn about Object-Oriented Programming (OOP) basics in C# with these 30 multiple-choice questions. Topics include classes, objects, constructors, destructors, properties, fields, and access modifiers.

---

Chapter 7: Object-Oriented Programming (OOP) Basics for C#

Classes and Objects

1. What is a class in C#?
   • a) A collection of variables
   • b) A template for creating objects
   • c) A method that performs a task
   • d) A special type of array
2. How do you create an object from a class in C#?
   • a) By using the new keyword
   • b) By defining a constructor
   • c) By creating a static method
   • d) By declaring a variable
3. What is the keyword used to declare a class in C#?
   • a) object
   • b) class
   • c) type
   • d) new
4. Which of the following is used to create an instance of a class in C#?
   • a) new ClassName();
   • b) ClassName();
   • c) create ClassName();
   • d) ClassName new();
5. What is the main purpose of an object in C#?
   • a) To store data
   • b) To define methods
   • c) To represent real-world entities
   • d) To perform arithmetic operations
6. What type of data does a class represent in C#?
   • a) Integer data
   • b) String data
   • c) Structured data (methods, properties, etc.)
   • d) Boolean data
7. How do you access an object’s property in C#?
   • a) Using dot notation
   • b) Using square brackets
   • c) Using parentheses
   • d) Using curly braces
8. What does the new keyword do when creating an object in C#?
   • a) Initializes the object
   • b) Declares the object
   • c) Assigns the object to a variable
   • d) All of the above

Constructors and Destructors

9. What is the purpose of a constructor in C#?
   • a) To initialize an object when it is created
   • b) To destroy an object when it is no longer needed
   • c) To define the class properties
   • d) To modify the object’s properties
10. Which of the following is true about constructors in C#?

• a) A constructor has the same name as the class
• b) A constructor can be called explicitly
• c) A constructor must return a value
• d) A constructor is not required in C#

11. What happens if no constructor is defined in a class in C#?

• a) The compiler automatically provides a default constructor
• b) An error occurs
• c) The class is incomplete
• d) The class cannot be instantiated

12. Which of the following is the purpose of a destructor in C#?

• a) To initialize objects
• b) To clean up resources when an object is destroyed
• c) To define properties
• d) To call methods on the class

13. What is the correct syntax for a destructor in C#?

• a) void DestructorName() { }
• b) ~ClassName() { }
• c) ClassName() { }
• d) ~DestructorName() { }

14. How is a destructor called in C#?

• a) Automatically when the object is no longer referenced
• b) Explicitly by the developer
• c) Using the Dispose method
• d) By invoking the Finalize method

15. What is the difference between a constructor and a destructor in C#?

• a) Constructors are used for initialization, destructors are used for cleanup
• b) Constructors are optional, destructors are mandatory
• c) Constructors are for classes, destructors are for objects
• d) There is no difference

16. How is a destructor related to the garbage collection process in C#?

• a) It explicitly frees up memory
• b) It helps to reclaim unused memory
• c) It is automatically called during garbage collection
• d) It does not interact with garbage collection

Properties and Fields

17. What is the main difference between a field and a property in C#?

• a) A field is a variable, while a property is a method that gets or sets a value
• b) A field is a constant, while a property is a variable
• c) A field cannot have a value, while a property can
• d) A field is always public, while a property is always private

18. Which of the following is the correct syntax for defining a property in C#?

• a) public int Age { get; set; }
• b) public int Age = 20;
• c) int Age { get; set; }
• d) public Age { int get; set; }

19. How are fields in C# typically declared?

• a) With a public access modifier
• b) Inside methods
• c) Inside constructors
• d) Inside classes with an access modifier

20. What keyword is used to declare a property in C#?

• a) private
• b) field
• c) property
• d) get/set

21. What is the default value of a field in C# if not initialized?

• a) 0 for numeric types, null for reference types
• b) 0 for all types
• c) null for all types
• d) false for boolean types

22. What is the advantage of using properties instead of fields in C#?

• a) Properties provide more control over how values are assigned or retrieved
• b) Fields allow better performance than properties
• c) Properties are easier to use than fields
• d) There is no advantage

23. Can a field in C# be made read-only?

• a) Yes, by using the readonly keyword
• b) No, fields are always read-write
• c) Yes, by using the private keyword
• d) No, fields cannot be read-only

24. Which of the following is true about properties in C#?

• a) A property can have different access levels for get and set
• b) A property must always have both get and set accessors
• c) Properties cannot be used to validate data
• d) Properties are not allowed in structs

25. Which of the following is a valid example of a read-only property in C#?

• a) public int Age { get; }
• b) public int Age { set; }
• c) public int Age { get; set; }
• d) public int Age { readonly get; }

Access Modifiers (public, private, protected, internal)

26. Which access modifier makes a member accessible only within its class?

• a) private
• b) public
• c) protected
• d) internal

27. What is the default access modifier for class members if none is specified?

• a) private
• b) protected
• c) public
• d) internal

28. Which access modifier makes a member accessible within its class and by derived classes?

• a) protected
• b) private
• c) internal
• d) public

29. What is the purpose of the internal access modifier in C#?

• a) It allows access to members within the same assembly
• b) It allows access to members from any class
• c) It restricts access to the class itself
• d) It restricts access to derived classes

30. Which access modifier allows a class member to be accessible from any code in the same assembly or outside it?

• a) public
• b) private
• c) protected
• d) internal

---

Answer Key

Qno	Answer
1	b) A template for creating objects
2	a) By using the new keyword
3	b) class
4	a) new ClassName();
5	c) To represent real-world entities
6	c) Structured data (methods, properties, etc.)
7	a) Using dot notation
8	d) All of the above
9	a) To initialize an object when it is created
10	a) A constructor has the same name as the class
11	a) The compiler automatically provides a default constructor
12	b) To clean up resources when an object is destroyed
13	b) ~ClassName() { }
14	a) Automatically when the object is no longer referenced
15	a) Constructors are used for initialization, destructors are used for cleanup
16	c) It is automatically called during garbage collection
17	a) A field is a variable, while a property is a method that gets or sets a value
18	a) public int Age { get; set; }
19	d) Inside classes with an access modifier
20	d) get/set
21	a) 0 for numeric types, null for reference types
22	a) Properties provide more control over how values are assigned or retrieved
23	a) Yes, by using the readonly keyword
24	a) A property can have different access levels for get and set
25	a) public int Age { get; }
26	a) private
27	a) private
28	a) protected
29	a) It allows access to members within the same assembly
30	a) public