1.2.4 Types of Programming Languages

Question 1

What do Procedural programs consist of

Answer 1

• Consist of statements that tell the computer exactly what to do and are executed line by line
• The basic module of a procedural program is the procedure which is a section of code that performs a task.
• Functions are also modules but they return a value

Question 2

What is a paradigm

Answer 2

• To describe an example of a way of doing things
• Styles of programming

Question 3

Why do programmers use procedural languages

Answer 3

• Because such languages enable them to focus on the logic problem rather than worrying about high level concepts such as software reuse.

Question 4

What are the key features of procedural languages

Answer 4

• Code is run serially, one line after another
• The language supports selection, iteration and assignment and sequence
• Code is developed in a modular way - blocks of code identifying set tasks
• Uses identifiers for variables, constants, prrocedures and functions
• Variables have either local or global scope

Question 5

What is Object-Oriented Programming

Answer 5

• Selection, iteration, identifiers for variables and constants are available in OO
• Procedures are replaced by classes, objects and methods
• Offers a more modular design, classes allow the developer to produce more reusable code .
• Captures a group of information data and related functionality into Objects

Question 6

What are the 3 characteristics that define an object-oriented language

Answer 6

• Encapsulation
• Inheritance
• Polymorphism

Question 7

In OO what are objects and classes

Answer 7

• Object - when you create an instance of a class. Each object that is instantiated from the same class will share the same attributes and methods.
• Class -A template (1) defining methods and attributes (1) used to make objects (1).

Question 8

What are the 3 main sections of a class

Answer 8

• Name of the class (light bulb)
• Attributes - information shared by any object in the class type (variable) (wattage, colour)
• Methods - code associated with the class, allows access or change to attributes (subroutines) (get Wattage () , get colour()

Question 9

What is Inheritance

Answer 9

• When a class takes on the methods and attributes of a parent class.
• The inheriting class may override some of these methods/attributes and may have additional extra methods and attributes of its own

Question 10

What is Polymorphism

Answer 10

• Something that occurs in several different forms.
• There are two main types of polymorphism in object-oriented programming - static and dynamic.
• Polymorphism means that objects of different types can be treated in the same way

Question 11

What is Static Polymorphism

Answer 11

• Allows you to implement multiple methods of the same name but with different parameters (within the same class)
• This process is known as method overloading
• The parameter must differ:
  
  • different number of parameters
  • The types of parameters need to be different (e.g 1 string, 1 integer)
  • Accept the parameters in a different order

Question 12

What is Dynamic Polymorphism

Answer 12

• Within an inheritance hierachy, a subclass is able to override a method of its superclass - this allows the code of the subclass to customise or completely replace the behaviour of that method
• This form of polymorphism - both methods share the same name and parameters, but provide different functionality depending on whether they are implemented by the superclass or subclass

Question 13

How do you create a class

Answer 13

• Classes in python are defined using the class keyword (class) and indentation.
• Methods are created using the def keyword.
• The biggest difference is that all methods must have at least 1 parameter called self and be inside the class indentation block.
• Self enables functions in Python access to attributes and methods of the class

Question 14

How do you use attributes and inheritance in python

Answer 14

1. Attributes must be defined in order for them to be part of the class
   * Occurs in the _init_(self) method - called when the class is instatiated. Known in OO terms as a constructor
2. The base class must be defined first. Put the name of the class in brackets after the name of the subclass. class Scientific (Calculator)

Question 15

What is assembly language

Answer 15

• An assembly language is a low-level programming language for a computer in which there is 1-1 correspondence with the language and machine code instructions
• Each assembly language is specific to a particular computer architecture

Question 16

What are some of the mnemonics used in Assembly language

Answer 16

• ADD - add number to the accumulator
• SUB - subtract a number from the accumulator
• MUL - multiply a number to the accumulator
• JMP - jump to memory address and start executing from there
• Assembly language also uses labels to represent variables and memory addresses. When the program is assembled, these labels are converted into memory address using a symbol table

Question 17

What are the 4 different types of addressing modes

Answer 17

• Immediate addressing mode
• Direct addressing mode
• Indirect addressing mode
• Indexed addressing mode

Question 18

What is immediate addressing mode

Answer 18

• The value in the address part of the instruction is actually the value to be used. Memory doesnt need to be searched to find the required value
• ADD 10 “means add 10” not value in address 10

Question 19

What is direct addressing mode

Answer 19

• The value in the address part of the instruction is a reference to the address in memory where the required value is located
• For example ADD 10 means “Go find address location 10, add what you find to the accumulator”.

Question 20

What is Indirect Addressing mode + an advantage

Answer 20

• The value in the address part of the instructon is a reference to a memory location that contains the address in memory where the required value is required
• Example) ADD 10 means “Go to memory address location 10. There you will find another address. Go to this address and add what you find to the accumulator.
• This mode of addressing is useful - larger address range can be used to reference data/instruction

Question 21

What is Indexed Addressing Mode

Answer 21

• More efficient to use an index register (IR) instead of repeating instructions
• The IR is set to 0 - 10+ 0
• After, IR is incremented 10+ 1
• An array needs to be stored in contigious memory locations
• ADD 10 means go find memory address location 10. Plus the value in IR (3). Go to memory address 13 and add the number you find there.

Question 22

Can you use variables in assembly language

Answer 22

• You can use variables in assembly language. No worry about memory addresses
• Allows you to perform valuations . Uses direect addressing to replace val

Question 23

What are Jumps and Compares

Answer 23

• Both allow flow control within assembly language and provide basic functionality of loops and decision statements and functions as found in higher level languages val = 3, if val=3 then
• Jump instructions allow control to move to a different part of the program specified by a memory address. There are 2 types: unconditional - always jumps and conditional - uses a compare instruction

Question 24

Why are labels used

Answer 24

• Labels are used to specify the destination of a jump instruction.
• A jump command needs to have a label in order to exactly know where in the code it must jump to. Labels must be converted to memory addresses in assembly

Question 25

What is calling the Kernel

Answer 25

• In assembly language programming, neccessary to invoke kernel code to perform tasks such as file handling or printing.
• An invocation of kernel code is known as a system call. Each system call needs values in specific registers then make a software interrupt (32 bit) or issue a syscall (64 bit)
• The Kernel is responsible for dealing with interrupts, how 32 bit Assembly code communicates to the Kernel (can be slow - perform many memory lookups
• The syscall method in 64-bit code uses specific registers to speed invocation

Question 26

What is a stack

Answer 26

• When an assembly language program is loaded, a stack that contains information about the command - line options is created.
• The stack is stored in memory and can be manipulated by registers or by instructions push and pop.
• When a program loads, the stack will contain any command-line arguement
• The number of items in a stack is always 1 or more even if there are no arguements (name is added)

Question 27

What is Little Man computer

Consider relationship between assembly language code and the LMC

Answer 27

• Considered a RISC (Reduced Instruction Set Computing)
• Ecah instruction has a simple opcode and makes use of direct addressing
• Data is stored and used within programs using variables.
• LMC uses mailbox to be equivalent to memory
• FDE not used explicitly. Each version displays PC and ACC

Question 28

What is opcode?

Answer 28

Part of the instruction / code

Indicates what to do

Question 29

How are branches used in LMC

Answer 29

• Iteration and selection in procedural languages are implemented in machine code using branches (jumps)
• In order to implement the condition for a while a loop - need to use 2 branches - 1 loop to start and 1 to break iteration
• LMC has only 2 conditional branches - branch if value in accumulator is positive or 0.

Question 30

EXAM QUESTION: Explain what is meant by “Encapsulation”

Answer 30

• When an attribute is made private so can’t be directly accessed to or changed from outside the class
• Public methods are used to read/ amend the attributes value
• Bundling the data with the methods that operate on it and prevent unauthorised access to values so they can’t be accessed or changed

Question 31

EXAM QUESTION: What are the advantages of Encapsulation

Answer 31

• Reduces the chances of errors/ inconsistencies
• Ensure objects can only be changed in the way intended and are consistent in the way they should behave
• Protecting data/ can’t be changed accidentally

Question 32

What is the process of making a new object?

Answer 32

• Instantiation
• When a new object is created a blank version is generated in memory and reference to is returned.
• The new keyword is responsible for making a class and allocating memory. Attributes can be made using this reference

Question 33

Exam Question: What is the difference between STA and LDA instruction?

Answer 33

• STA store the value in the accumulator into a given memory location
• LDA loads the value in a memory location into the accumulator.

Question 34

What are some advantages of using object-oriented techniques?

Answer 34

• Breaking a problem down into objects as different team members can work on different objects.
• Inheritance means that one class can be coded and that code used as the base for similar objects. This will save the team time
• Encapsulation means that objects only interact in the way intended and prevents unexpected changed to attributes. This means there are likely to be fewer issues as the team combines their code.
• Polymorphism means that code can be written that is able to handle different objects in the same way. This reduces the volume of code the team need to produce.

Question 35

Exam Question: Describe three features of an object-oriented language.

Answer 35

• Self-contained object / (instance of a) class / entity / real world object …
  
  • … contains routines / methods / attributes / data
• Program split into small units/object…
  
  • … which are used (by other objects) to build a complex system
• Uses encapsulation…
  
  • …to hide data within objects / object only accessed through methods
• Inheritance…
  
  • … / superclass / subclass / derived classes