1.4 Principles of programming

Question 1

What are meta languages and why are they preferable to using natural English

Answer 1

meta language - a language which describes the syntax of another language (e.g. BNF, syntax diagram)

They are preferable to natural languages as they are unambiguous (sentence has one meaning) which is good for the computer as it needs to know precisely what it is being asked to do when running the program

Question 2

define syntax

Answer 2

rules of a particular programming language

Question 3

do bnf questions

Question 4

do syntax diagram questions

Question 5

why do programming languages need to be unambiguous and compare to natural language

Answer 5

programming languages need to be unambiguous because:
-computers have to know exactly what it is being asked to do

this is unlike natural languages which are ambiguous

Question 6

what is a programming paradigm and describe the various paradigms

Answer 6

programming paradigm - a fundamental structure and approach of a programming language

Types:
Procedural languages - (e.g. C++) written as an ordered set of instructions in a sequence that the computer follows strictly i.e. actions/calculations/selection/iteration/procedure calls in order

Non-procedural languages - (e.g. PROLOG) allows programmers to specify the results they want without having to solve the problem. The program is written as a list of facts and rules. Used for making AI like expert systems.

Event-Driven programming - (e.g. sensors monitoring heat) more often part of a visual programming language, rather than one main subroutine that runs and calls other subroutines, subroutines are written to react to events that occur e.g. button press

Visual Programming - (e.g. visual basic) allows rapid, easy development of professional-looking applications which reduces the need for typical programming

Mark-up languages - (e.g. HTML) not really a programming paradigm, but are a key part of web programming. They add commands to a text document to add further meaning to the text or to structure it (e.g. titles)

Object-oriented programming - ability to combine data and the procedures that use the data into one object, makes the program easier to maintain and understand as the object complexity can be hidden from the program.

NOT MUTUALLY EXCLUSIVE - CAN BE MULTIPLE (e.g.visual basic event driven, visual and object oriented)

Question 7

Define inheritance

Answer 7

easy to re-use objects in other programs and if necessary create new objects that inherit from other objects without having to recode.

Inheritance enables new objects to take on the properties of existing objects

It is when a new class is created that is based on another class

It can take on the methods and attributes of the parent class

Question 8

what are the features of a low level language

Answer 8

e.g. assembly language which is usually specific to the type of processor on which the program needs to run

programmers have to write the software in a ‘computer-centric’ way, interacting directly with registers, memory locations, etc.

one low level instruction translates into one machine code instruction, therefore will run faster. They are also programs smaller in size.

Slower and more difficult to program

Uses more cryptic and harder to understand references to memory locations and sections of code (i.e. contains no self-documenting identifiers)

time to convert to machine code (using an assembler) is negligible so can run immediately

Question 9

what are the features of a high level language

Answer 9

e.g. Java, Python, VB which is available on many different computer architectures.

a compiler translates the source code into machine code

Programmer works in a more ‘human-centric’ way, not requiring direct access to the internal registers of the processor. Closer to spoken english semantics

One line of code translates into many lines of machine code, compiler will generally not translate into as few machine code instructions as a hand-crafted low level program

Easier to program and programs that translate into hundreds of machine code instructions can be rapidly created.

has self-documenting identifiers

requires compilation before code can be run for the first time

easier to create modules that can be re-used and accessed by other parts of the program

allow the use of powerful commands that can perform quite complex tasks

Question 10

what is standardisation, why is it useful to standardise computer languages and explain the difficulties of doing to

Answer 10

Most languages started out standardised e.g. basic -> then different companies added extra functions and commands to produce various different variants -> e.g. Quick Basic, BBC basic, Visual Basic, etc.

Difficult to agree standards as it takes time, languages need to develop and evolve new features as computers become more powerful and new tech appears

Programming in a popular language is a good idea-> compilers available for many different systems -> companies fan more easily create different versions of their software for different operating systems

Makes it easier for companies to employ programmers that are already skilled in a particular language (programmers are in demand)

Question 11

define class

Answer 11

is used in object-oriented programming

A template defining methods and attributes used to make objects

Question 12

define object

Answer 12

The definition of an object is known as a class

is used in object-oriented programming

Are created for things that the program needs to manage e.g. student as an object

Contains:
-data fields (attributes) about the object, such as StockID, Description, etc.

-subroutines/procedures that can be performed on the object e.g. Addstock, DisplayQuantitySold, etc.

Question 13

define attributes

Answer 13

is used in object-oriented programming

Data fields about the object e.g. stockID, Description, etc.

Question 14

define methods

Answer 14

Subroutines/procedures that can be performed on the object

E.g. addstock, displayquantitysold

Question 15

what are the advantages of the object-oriented paradigm

Answer 15

Classes can be reused in future programs and objects can be created that inherit attributes and methods from another object but also gains its own methods such as Add_Exam_Scores

E.g.

Class student inherits from person Method Input_Exam_Results (exam, grade)
End method
..more methods
End class

Private attributes cannot be inherited still however protected can be

Ability to combine data and procedures that use the data together in one object is more intuitive

Encapsulation makes the program easier to maintain and understand (complexity is hidden from program/people that use it)

Abstraction is similar to encapsulation but it means that we allow access only where necessary to the encapsulated data via public or protected methods/attributes

Inheritance: easy to reuse objects in other programs and if necessary create new objects that inherit from other objects without having to recode

E.g. gears in a car are encapsulated (hidden), Abstraction is provided via a gearstick to allow the driver to change gears

In visual languages, new custom controls can be created, inheriting all the methods and attributes of a normal listbox

Question 16

what does an object consist of?

Answer 16

-Data fields
-Subroutines/Procedure

Question 17

What are the disadvantages of object oriented programming?

Question 18

Define Public, Private, protected attributes and methods and explain the difference between them

Answer 18

Public attributes can be accessed anywhere as its public and inherited

Protected attributes can be accessed through inheritance but I’d private in every other case

Private attributes can be accessed through methods in subclass

Question 19

define instantiation

Answer 19

Creating a new object

Question 20

define abstraction

Question 21

define encapsulation

Answer 21

All attributes and methods related to one thing kept together in a single object

(Effectively another form of modularisation and black-box programming)

Question 22

Look at UML class diagrams

Question 23

explain the nature of procedural and non-procedural programming paradigms and their application

Question 24

explain the advantages of using a procedural language to write a program based on an algorithm

Question 25

explain the features of the mark-up language programming paradigm

Question 26

explain the features of event-driven language

Question 27

explain the features of visual programming languages

Question 28

How do you create an object variable of value b based on the class person

What can it then be used to do

Answer 28

Define p as new person

Can now use the public methods of the object

E.g. p.InputDetails(“Smith”,”Janet”,”12/5/1990”)

And public attributes

E.g. p.surname

But cannot access any private or protected attributes

Question 29

What is different about protected and private attributes compared to public

Answer 29

Protected and private attributes and methods are accessible only within the class.

However, protected attributes and methods can be used by derived classes that inherit from the class

Question 30

Explain instantiation

Answer 30

A class (which acts like a template)

Instantiate, so declares a variable object based on the class template

So e.g. a variable p1 has all the public properties within the class (variables, methods)

Can do stuff like p1.surname = “smith” and the property surname for that object is changed to smith

Another one is p1.AddToFile(“students.txt”) is a public method which will he called and students.txt will be sent to it

Question 31

What is a superclass

Answer 31

It is a term given to the parent class

Question 32

What is a subclass

Answer 32

The derived class

Question 33

What is UML

Answer 33

Unified modelling language

Often used in class diagrams to describe classes and inheritence:
Example:
________________________
| Vehicle |
|——————————‐|
|-Manufacturer :String |
|#Price :Real |
|+colour : string |
|——————————‐|
| +GetManufacturer() |
|+GetPrice |
|——————————‐|
Top box:name of class
Middle box:list of attributes
Bottom box: list of methods

• denotes a private attribute or method
  + denotes a public attribute or method
  # denotes a protected attribute or method

Question 34

What is a reason that methods in subclasses are required

Answer 34

There could be a private attribute that couldn’t be inherited from the superclass so a method is developed to allow the private attribute to be given a value

Question 35

What is a reason that methods in subclasses are required

Answer 35

There could be a private attribute in attribute so cannot be set directly

Question 35

What is a reason that methods in subclasses are required

Answer 35

There could be a private attribute in the subclass so cannot be set directly

Requires a publicly available method

Question 36

What does inheritance enable

Answer 36

Classes that are similar to existing classes can be created by indicating differences (rather than starting again) and thereby allowing code to be organised and reused effectively

Question 37

What does inheritance define

Answer 37

It defines relationships between classes and organises classes into groups

Question 38

What is polymorphism

Answer 38

Allows a derived class to provide its own version of a method from the superclass

I.e. subclasses can override the inherited superclass method with their own

Question 39

What are the differences between natural language and computer languages

Answer 39

Natural languages are ambiguous I.e. there can be more than 2 meanings to a sentence

Computer languages are designed to be unambiguous I.e. 1 meaning and the computer needs to know precisely what is being asked to do when running

The rules of how a particular language is structured is known as the syntax of the language

Because a computer language is unambiguous the syntax rules of the language can be defined using a meta language

Question 40

What is the purpose of BNF

Answer 40

To describe unambiguously the syntax of the computer language