Lecture 3: Introduction to Classes in C++

Question 1

Concept of classes in OOP

Answer 1

• Classes in OOP: parts of code that form the elements of the programs
	○ While the program is executed, instances or "objects" of the class are made which are essentially pieces of software which model and behave like real-life objects
		§ They can interact with one another using functions to solve the given problems
        ○ A main skeleton or blueprint from which individual objects are created
		§ Contain member variables to represent attributes and member functions to represent behavior and/or state

Question 2

What is the principle of abstraction and how does it relate to OOP?

Answer 2

• Principle of abstraction: Capture only the details that are relevant to the current perspective
○ All other details are omitted
○ A class can be made on the basis of those details
E.g. a map may need to show roads, but it does not need to show sewage pipes

Question 3

What are the advantages of abstraction?

Answer 3

Any details can be picked 
Provides a skeleton for the class of objects

Question 4

Access specifiers

Answer 4

a keyword that determines what kind of access is given to the main program for each class member, variable or function

Question 5

Private

Answer 5

Only within the functions of the same class

Question 6

Protected

Answer 6

accessible to functions of the same and derived classes

Question 7

Public

Answer 7

anywhere where the object is accessible

Question 8

Difference between structures and classes

Answer 8

Default access specification:
Private for classes
Public for structures

Question 9

Member functions

Answer 9

perform actions on the data members of the class, and are part of the class

Question 10

Public member functions

Answer 10

provide an interface with the private members of the class

Question 11

How is the concept of data encapsulation used in classes?

Answer 11

Public access is only used for member functions
○ Public access of variables goes against the fundamental OOP concept of data encapsulation - Data must be hidden from direct view

Question 12

4 common types of member functions

Answer 12

setters
getters
constructors
destructors

Question 13

What is inlining?

Answer 13

Instead of jumping to the function definition from the point of function call, the compiler places a copy of the inline function at the call point

Question 14

Inlining may not always be performed. Explain why.

Answer 14

○ A REQUEST, not a command to the compiler
May not perform inlining if the following are present:
□ Loop
□ Static variables
□ Recursive functions
□ Switch/goto statement

Question 15

Advantages of inlining

Answer 15

Function call overhead doesn’t occur, so saves time, memory and power
More effective for smaller functions
Saves the overhead of push/pop variables (Push: )
Saves overhead of return from a function

Question 16

Disadvantages of Inlining

Answer 16

Too many inlined functions increase the size of the binary executable (The same code is copied)
Increases compile time overhead for larger functions (functions more than a line)
All calling locations have to be recompiled if the code in the definition is changed
Takes a lot of memory
In many systems, the size of the code is more important than speed

Question 17

Constructor

Answer 17

a function to ensure that the object is in a well-defined state at the time of creation
Automatically called when a new object is created - cannot be explicitly called

Question 18

If more than one object is created, in what order are the respective constructors called?

Answer 18

In the order the objects are declared

Question 19

3 types of constructors

Answer 19

Default
Parameterized
Copy

Question 20

Default constrcutor

Answer 20

Created automatically if we don’t make one (default or otherwise)
Used to assign default values or dynamically make memory

Question 21

Parameterized constructor

Answer 21

Has some arguments

Used to assign values to data members

Question 22

Destructor

Answer 22

Called when object passes out of scope or is explicitly deleted
Used to de-allocate and free memory
No arguments
Cannot be overloaded
Default created if we don't provide one

Question 23

If there is more than object, in what order are the destructors called?

Answer 23

Reverse order of declaration