Section A — 1 Mark Questions
1. Define a constructor. [1 Mark]
Answer: A constructor is a special member function of a class that is automatically invoked when an object of that class is created.
2. What is the primary purpose of a constructor? [1 Mark]
Answer: The primary purpose of a constructor is to initialize the data members of an object.
3. Does a constructor have a return type? [1 Mark]
Answer: No, a constructor does not have any return type, not even void.
4. What is a default constructor? [1 Mark]
Answer: A constructor that accepts no arguments is called a default constructor.
5. What is a parameterized constructor? [1 Mark]
Answer: A constructor that accepts one or more arguments to initialize objects with user-defined values is a parameterized constructor.
6. How is a copy constructor defined? [1 Mark]
Answer: A copy constructor is a constructor that initializes an object using another object of the same class.
7. What is the symbol used for a destructor? [1 Mark]
Answer: The tilde symbol (~) is used to prefix the destructor name.
8. When is a destructor called? [1 Mark]
Answer: A destructor is called automatically when an object goes out of scope or is explicitly deleted.
9. Can a class have more than one constructor? [1 Mark]
Answer: Yes, a class can have multiple constructors through constructor overloading.
10. What is a dynamic constructor? [1 Mark]
Answer: A dynamic constructor is used to allocate memory to objects during runtime using the new operator.
11. Must a constructor have the same name as the class? [1 Mark]
Answer: Yes, a constructor must have the exact same name as the class it belongs to.
12. What happens if no constructor is defined in a class? [1 Mark]
Answer: The compiler automatically provides an implicit default constructor.
13. Can a constructor be private? [1 Mark]
Answer: Yes, a constructor can be declared as private, typically used in Singleton design patterns.
14. Are constructors inherited? [1 Mark]
Answer: No, constructors are not inherited by derived classes.
15. What is constructor overloading? [1 Mark]
Answer: Constructor overloading is the process of having multiple constructors with different parameter lists in the same class.
16. Can a destructor be overloaded? [1 Mark]
Answer: No, a destructor cannot be overloaded; there can be only one destructor per class.
17. What does a copy constructor take as an argument? [1 Mark]
Answer: It takes a reference to an object of the same class, typically as a const reference.
18. Is a destructor called for static objects? [1 Mark]
Answer: Yes, it is called when the program terminates.
19. Can constructors be called explicitly? [1 Mark]
Answer: Yes, constructors can be called explicitly in code, though it is unusual.
20. What is the main difference between a constructor and a destructor regarding arguments? [1 Mark]
Answer: Constructors can accept parameters, while destructors cannot accept any parameters.
Section B — 2/3 Mark Questions
1. Explain the concept of constructor overloading. [2 Marks]
Answer: Constructor overloading occurs when a class has multiple constructors with different parameter lists. This allows objects to be initialized in different ways depending on the arguments passed during object creation.
2. Differentiate between default and parameterized constructors. [2 Marks]
Answer: A default constructor takes no arguments and initializes objects with default values. A parameterized constructor takes arguments to initialize objects with specific user-provided values.
3. Why is a copy constructor necessary? [3 Marks]
Answer: A copy constructor is necessary to create a new object as a copy of an existing object. It ensures that deep copies can be performed if the class manages resources like pointers, preventing shallow copy issues where two objects might point to the same memory location.
4. Explain the role of a destructor. [2 Marks]
Answer: The role of a destructor is to clean up resources such as memory, file handles, or database connections that were allocated during the lifetime of an object, thus preventing resource leaks.
5. What is a dynamic constructor and why is it used? [3 Marks]
Answer: A dynamic constructor uses the 'new' keyword to allocate memory at runtime. It is used when the size of the data or the requirement for memory is unknown at compile time, allowing for flexible memory management.
6. State two rules for defining constructors. [2 Marks]
Answer: 1. The constructor name must be the same as the class name. 2. It must not have any return type (not even void).
7. Can a destructor be private? Explain. [2 Marks]
Answer: Yes, a destructor can be private. This is sometimes done to control the object's lifecycle, for instance, to prevent the object from being destroyed by the user or to enforce heap allocation.
8. What is the difference between shallow copy and deep copy in the context of copy constructors? [3 Marks]
Answer: A shallow copy simply copies the values of members (including addresses of pointers), leading to multiple objects sharing the same resource. A deep copy allocates new memory and copies the actual contents, ensuring each object manages its own unique resource.
9. How are multiple constructors handled in a class? [2 Marks]
Answer: Multiple constructors are handled through constructor overloading, where the compiler selects the appropriate constructor based on the number and type of arguments provided during instantiation.
10. Explain when a destructor is called in the case of multiple objects. [3 Marks]
Answer: Destructors are called in the reverse order of object creation. If objects are created in a specific stack or local scope, the destructor for the most recently created object is called first when exiting that scope.
Section C — 5 Mark Questions
1. Explain the concept of a Copy Constructor in detail with an example. [5 Marks]
Answer:
Introduction
A copy constructor is a special member function used to initialize an object from another existing object of the same class.
Need for Copy Constructor
When an object is passed by value, returned by value, or initialized using another object, the default copy constructor performs a member-wise copy. For classes involving dynamic memory, this can lead to errors like double-freeing memory.
Syntax and Example
The copy constructor takes a reference to the same class: ClassName(const ClassName &obj).
Example: MyClass(const MyClass &obj) { data = obj.data; }
Key Points
- It must take a reference argument, otherwise, it would trigger an infinite loop of calls.
- The argument is usually marked 'const' to prevent modification of the source object.
- It is essential for deep copying pointers to prevent memory corruption.
2. Describe the features and usage of parameterized constructors. [5 Marks]
Answer:
Introduction
Parameterized constructors allow developers to pass arguments to the constructor at the time of object creation, enabling custom initialization of data members.
Features
- They accept one or more parameters.
- They can be overloaded to provide multiple ways to initialize an object.
- They enable the passing of initial state values during object instantiation.
Usage
When an object is declared, values are passed in parentheses: ClassName obj(value1, value2);. This invokes the specific constructor matching the signature. This is highly useful for initializing variables with specific data rather than default values, making the object ready for use immediately upon creation.
Advantages
It enhances code readability and ensures that no object remains in an uninitialized or indeterminate state, which is a common source of runtime bugs.
3. Compare and contrast Constructors and Destructors. [5 Marks]
Answer:
| Feature | Constructor | Destructor |
|---|---|---|
| Name | Same as Class | Same as Class with ~ prefix |
| Purpose | Initialize object | Destroy object / Release memory |
| Parameters | Can have parameters | Cannot have parameters |
| Overloading | Can be overloaded | Cannot be overloaded |
| Invocation | Called automatically on creation | Called automatically on destruction |
Explanation
While the constructor acts as the entry point for the object, preparing it for use, the destructor acts as the exit point, ensuring no memory leaks occur. Constructors can be overloaded to provide flexibility, whereas the destructor is unique because it must perform cleanup without ambiguity.
4. Discuss the purpose and implementation of Dynamic Constructors. [5 Marks]
Answer:
Introduction
Dynamic constructors use the 'new' operator to allocate memory dynamically for an object's member variables at runtime.
Need
When the memory requirements for an object are not known at compile time, such as handling strings of variable length or dynamic arrays, static allocation is insufficient. Dynamic constructors provide the flexibility to request memory based on the specific needs of the instance.
Implementation
The constructor typically declares a pointer member and uses the 'new' operator: ptr = new int[size];. It is crucial to have a corresponding destructor that uses the 'delete' or 'delete[]' operator to release this allocated memory to prevent leaks.
Conclusion
Using dynamic constructors is a fundamental practice in C++ for managing resources that persist beyond the scope of a single function call, but it demands careful handling of memory to ensure stability.
5. Explain the role of multiple constructors in a class with an example. [5 Marks]
Answer:
Introduction
Multiple constructors allow a single class to provide different ways of initializing objects, known as constructor overloading. This makes classes versatile and user-friendly.
Mechanism
The compiler differentiates between constructors based on their signature (the number and types of parameters). When an object is created, the C++ compiler matches the provided arguments with the available constructor declarations.
Example
A 'Rectangle' class might have:
- A default constructor setting dimensions to 0.
- A parameterized constructor setting width and height.
- A copy constructor to clone an existing rectangle.
Conclusion
By providing multiple constructors, a class can support different scenarios, such as creating an empty object, a fully specified object, or a duplicate object, effectively managing the initialization logic based on user needs.