2.2.1 - Programming Techniques

Question 1

What is a variable?

Answer 1

• Identifier of a memory location used to store data
• Used to store a value which can change during execution

Question 2

What are the global variables?

Answer 2

• The variable can be accessed throughout the scope of the program (visible throughout a program)
• Using passing by reference is an equivalent of a global variable.

Question 3

What are the negatives of global variables?

Answer 3

• Uses more memory - memory is declared when the program starts and remains in use throughout.
• Testing more difficult - it is difficult to test an individual block of code.
• Reduces data accuracy - Changing a global variable may have an impact on another module.

Question 4

What are the positives of global variables?

Answer 4

• Simpler to program - values do not need to be passed between different subroutines.
• Do not need to worry about returning values - all parts of the program can access the value.

Question 5

What is a local variable?

Answer 5

• Can only be accessed within the scope of the sub-program where it is created
• A parameter that is passed into a subroutine becomes a local variable in the subroutine e.g. LoadLevel(Difficulty)

Question 6

What is an IDE?

Answer 6

Integrated Development Environment (IDE) - A program used for developing programs, made from several components.

Question 7

Describe and explain the tools that are provided by an IDE to develop software

Answer 7

• Auto-complete – Will predict variable and built-in functions and finish off the word. Can avoid spelling mistakes and speed up development
• Syntax highlighting (colour coding text) - Can distinguish between different features quickly to check code is correct
• Auto Indent – Indents code automatically within structures to avoid errors

Question 8

Describe and explain the tools that are provided by an IDE to debug software?

Answer 8

• Error highlighting - Syntax errors highlight dynamically so they can be corrected before running the program (saving time)
• Variable Watch window – Display the values of the variables during running of the program
• Break points- Stop the program at set points to check the values of variables. Developer can add multiple breakpoints.
• Error message list- Tells you where errors are and suggests corrections
• Stepping - Executes program one line at a time to watch variable values and program pathways
• Traces - Printouts of variable values for each statement execution

Question 9

What are the three programming constructs?

Answer 9

Sequence

Selection / Branching

Iteration

Question 10

What is an example of a count controlled loop?

Answer 10

FOR Loop - Will run for a set number of predetermined times.

Question 11

What is an example of a condition controlled loop?

Answer 11

WHILE / DO WHILE - Will run whilst a condition is true or false

Question 12

What is the difference between a WHILE loop and a DO loop?

Answer 12

• While loop will check the condition at the start of the loop - this means the code may never run
• Do loop will check the condition at the end of the loop - this means the code will always run at least once

Question 13

What are parameters?

Answer 13

• Parameters are the variables listed between the brackets, after the procedure/function name e.g.
• They become local variables in the routines that they are passed to.
• characterMovement(inputKey, characterx, charactery)

Question 14

What does passing by value mean?

Answer 14

By Value (ByVal)
* Does not override the original data
* A local copy of the data is used
* Data is discarded when the subprogram exits

Question 15

What does passing by reference mean?

Answer 15

By Reference (ByRef)
* Changes are made to the original data
* Memory location of data is sent
* Changes remain after the subprogram exits
* Uses less memory

Question 16

What is a function?

Answer 16

• A named block of code which always returns a value
• Uses the keyword return
• Assigns the returned value to a variable (e.g. y)

Question 17

What is a procedure?

Answer 17

• A named block of code which does not return a value
• Does not use the keyword return
• Is called by writing its name but not assigning the result to a variable

Question 18

What is modularity and what are the benefits of using it when writing code?

Answer 18

Breaking code down into functions / procedures / scripts

• Write once and call repeated times - Avoids repeated code.
• Can be tested individually and then added to the main program.
• Can be reused in other programs - No need to reprogram so saves time
• Can give sub-routines to different programmers to build concurrently
• Breaks problems into smaller areas. Small sub-programs are easier to read / understand / modify

Question 19

What is an OO class?

Answer 19

A template for defining methods and attributes, which is used to instantiate objects.

Question 20

What is an OO object?

Answer 20

An instance of a class which is created using a constructor (new)

Question 21

What is an OO method?

Answer 21

These are the actions that can be performed by an object; for example, get a position on a game board. Can get a value (getter) or set a value (setter)

Question 22

What is an OO attribute?

Answer 22

• Each object will have its own public or private attributes.
• The attributes of a player in a game of Monopoly might include its PlayerID and money.

Question 23

Define encapsulation and the benefits of using it.

Answer 23

• Attributes are set as private so they can only be accessed and changed via public methods
• Uses ‘set methods’ to modify the value of a private attribute
• Uses ‘get methods’ to retrieve the value of a private attribute
• Prevents unexpected changes to attributes having unforeseen consequences.

Question 24

Define inheritance

Answer 24

• A child class has its own attributes and methods, but it also gets all attributes and methods from the parent class.
• Uses the key word ‘inherits’ and ‘super’

Question 25

Define **polymorphism** (overriding)

Answer 25

* Code can be written that is able to handle different objects in the same way, this reduces the amount of code. * Using methods with the same name in a subclass as in a parent class is called overriding, which is a type of polymorphism. * Overriding allows a sub-class to use its own method rather than that of the parent.

Question 26

Write the **constructor** for the following class All objects have a **money** value of **2000**.

Answer 26

public procedure new(thePlayerID, thePosition) playerID = thePlayerID boardPosition = thePosition money = 2000 endprocedure

Question 27

Write the line to instantiate an object called "Boot" at position 10 using the Player class with the attributes **PlayerID, boardPosition, money** All objects have an unchangeable money value of 2000.

Answer 27

*ObjectName = new ClassName (attributes required)* Boot = new Player(“Boot”, 10)

Question 28

Write the pseudocode for the '**getter**' getPosition()

Answer 28

public function getPosition() return position end function

Question 29

Write the pseudocode for the '**setter**' setPosition()

Answer 29

public procedure setPosition (Theposition) position = Theposition end procedure

Question 30

How would you write a full **OO class declaration?**

Answer 30

classname **inherits otherClassName** (inheritance optional) private attribute1 ... public function getter() return attribute1 end function public procedure setter(aValue) attribute1 = aValue end procedure endclass

Question 31

What is **recursion**? Why does it need a **stopping condition**?

Answer 31

**Recursion is the process of a subroutine calling itself from within itself** A stopping condition must be included which when met means that the routine will stop calling itself and will start to 'unwind‘ No stopping condition would cause a ‘Stack Overflow’ error by filling the memory uncontrollably.

Question 32

What are the pros and cons of **recursive** algorithms?

Answer 32

(-) Too many calls may cause the program to run out of memory with a "Stack overflow" error (-) Each call produces a new local variable which means more memory spaces needed (+) Uses less lines of code and produces a more elegant solution

Question 33

What is **iteration**? What are the pros and cons of **iterative** algorithms?

Answer 33

Uses a loop to repeat instructions. There is an end condition to the loop which decides when to stop looping: * (+) Has no limit to the number of times it may be called. * (+) Only one copy of the variable is required. This means that less memory will be used * (-) Takes more lines of code and can be harder to understand

Question 34

What would be the output if 10 was passed as a parameter into this function?

Answer 34

(1 + 2 + 3 + 6 + 7 + 10) = **29**