Problem solving and programming

Question 1

Alpha testing (at least 4 properties)

Answer 1

Testing within the development company //
testing by the developers
Testing it in the way the end user would
Used when the program is complete
Used when white box/black box/system etc.
testing is complete
Takes place before Beta testing

Question 2

Advantages of global variables (2 x AO1, 2 x AO2)

Answer 2

Simpler to program …
… because values do not need to be
passed/renamed/moved between different
subroutines
Do not need to worry about returning values //
do not need to decide between byval/byref …
… all parts of the program can access the
(same) value (in the same way)

Question 3

Disadvantages of global variables (3 x AO1 and 3 x AO2)

Answer 3

Uses more memory …
… because the memory space is declared when the program starts and remains in use throughout (negligible for small programs)
Makes testing / debugging more difficult …
…. as it’s difficult to test an individual block of code
Reduces data accuracy / integrity …
…. changing a global variable may have an impact on another module

Question 4

IDE for debugging (AO1 and AO2, at least 3)

Answer 4

-Debugging tools (variable watchers) allow inspection of variable values, this can allow run-time detection of errors
-Code can be examined as it is running, which allows logical errors to be pinpointed
IDE debugging can produce a crash dump, which shows the state of variables at the point where an error occurs
-It can step through code, which allows the programmer to (watch the effects of each line of code and) check variables
-The insertion of a break-point, allows the program to be stopped at a predetermined point in order to inspect state of variables

Question 5

What is a function

Answer 5

-A function is a named section of program (1) that performs a specific task (1).
-It returns a value (1), it is often called inline (1).

Question 6

What is recursion

Answer 6

The function calls itself from within the function

Question 7

Recursion > iteration

Answer 7

-More natural to read (1)
-Quicker to write / less lines of code, (1) as some functions are naturally recursive (1)
-Suited to certain problems (1), for example those using trees (1)
-Can reduce the size of a problem with each call (1)

Question 8

Recursion < iteration

Answer 8

-Can run out of stack space / memory (1) (due to too many calls (1)) causing it to crash (1) This can be avoided with tail recursion (1)
-More difficult to trace / follow (1) as each frame on the stack has its own set of variables (1)
-Requires more memory than the equivalent iterative algorithm.
-Usually slower than iterative methods (1) due to maintenance of the stack (1)

Question 9

Difference between global and local variables

Answer 9

Global variable is visible throughout a program / may be accessed from more than one part of the program (all subroutines) (1), local variable is visible only in module construct where it is created / declared (1)

Question 10

Properties of local variables (at least 3/4)

Answer 10

-Local variables are created in the subroutine they are
created in, they are not accessible directly from any
other subroutine
-Local variables are removed from memory when the
subroutine ends.
-Local variables can be passed as parameters to a
function to be updated, and then returned to override
the original local variable
-Local variables can be passed by reference to a
subroutine to allow the content of the variable to be
updated

Question 11

Black box testing

Answer 11

Checks that given inputs give the correct output
No understanding of the code (not looking at the code)

Question 12

White box testing

Answer 12

Understands the structure and logic of the program
Each line/path of code is tested

Question 13

Inspection (testing)

Answer 13

During a meeting a small team will read through code
Analysing it with a checklist which list the common problems

Question 14

What is IDE (integrated development environment)

Answer 14

A single program (1) used for developing programs (1) made from a number of components

Question 15

When must a global variable be used

Answer 15

A global variable used where a value needs to be accessible from various parts of a program (1 – AO 1.2), it is the same value (1 – AO 1.2).
Irrespective of the place where it is accessed (1 – AO 1.2).
e.g. today’s date, VAT rate, pi (1 – AO 2.1).

Question 16

Functions vs procedures

Answer 16

A function returns a single data type value (1), whereas a procedure can pass back many values (1) by parameter (1)
A function can be used in line (as part of a statement)
A function can be used as a variable
A procedure is used as any other program instruction

Question 17

What is a variable

Answer 17

A memory location
That stores data/a value
That can be changed

Question 18

OOP - what is a class

Answer 18

A class is a template (1) used to define methods and attributes (1) used to make objects

Question 19

OOP - what is inheritance

Answer 19

Inheritance is when a child class takes on all attributes (1) and methods (1) from a parent class (1). The inheriting class may override some of these methods / attributes (1) and may have additional extra methods and attributes of its own (1)

Question 20

OOP - what is encapsulation

Answer 20

Encapsulation is the process of keeping an object’s attributes private so they can only be accessed and changed via public methods

Question 21

OOP - what is an object

Answer 21

An object is an instance of a class

Question 22

OOP - what is an instance

Answer 22

An instance is a specific occurrence of a class

Question 23

OOP - how to make attributes private (python)

Answer 23

Double underscore after the dot
e.g. “self._ _name = name”

Question 24

OOP - what is polymorphism

Answer 24

Polymorphism means that objects of different types can be treated in the same way

Question 25

Backtracking, definition and example (textbook)

Answer 25

-An approach to finding a solution that explores a possibility until it is no longer deemed feasible. At this point we "backtrack"/undo the last step to return to the last point at which it worked and follow a new path Examples: DFT, chess

Question 26

Data mining, definition and purpose

Answer 26

-Analysis of patterns and anomalies in large data sets -Turns large quantities of data into useful information. These may not be immediately obvious to a **casual reader**. -Resulting information is used to make predictions, to increase revenue, to target advertising and improve services.

Question 27

Data mining, disadvantages/limitations/things to consider (at least 3)

Answer 27

-Data mining can spot patterns/trends, however it cannot explain them. Company may still need to do extra research. -Requires powerful computers with a lot of processing power to process huge amounts of data. -Need to make sure data collection is legal and in terms and conditions -Analysis can be costly e.g. may need an external company -Security - data being collected requires protection

Question 28

Conceptually, what is passing by value (textbook)

Answer 28

Passing by value sends a **copy** of the value to the subroutine

Question 29

Conceptually, what is passing by reference (textbook)

Answer 29

Passing by reference send the **memory location** of the argument to the subroutine meaning the parameter points to that location

Question 30

IDE features for writing a program

Answer 30

1 mark per identification 1 mark for expansion, max 2 each. Write: e.g. * Auto-complete * Start typing an identifier/command and it fills in the rest * Auto-indent * Indents code automatically within structures to avoid errors * Coloured command words // pretty printing // syntax highlighting * Shows which commands are correct // help identify key elements

Question 31

Two features of any recursive program

Answer 31

* A function that calls itself // a function that is defined in terms of itself * …has a base case (that terminates the recursion)

Question 32

OOP vs Procedural AO1

Answer 32

**AO1: Knowledge and Understanding Indicative content** * OOP defines an object as an independent entity * OOP defines the attributes of the object and the methods that can be applied to it * attributes could be private to restrict accidental changes * Procedural the statements are executed in the order they are written

Question 33

Advantages of OOP over PP for several of the same structures (AO2)

Answer 33

*OOP allows for an object to be created from the structure * Many instances of this structure can then be declared in the main program. * Procedural will need each structure to be declared individually * Procedural will need to make use of subroutines where the structure will need to be sent and returned each time.

Question 34

Advantages of OOP over PP for several of the same structures (AO3)

Answer 34

* OOP reduces amount of code needed therefore fewer errors are likely as code is written once and then used multiple times * OOP can reduce mistakes because the subroutines are self-contained. In procedural it would need to make sure the correct values are passed and returned, or global variables may be required which uses excess memory

Question 35

Items of data to obtain before developing app

Answer 35

 Popularity data (1).  Platforms available (1).  Sales of existing similar apps (1).  Prices charged (1).  Does it exist already? (1).

Question 36

Describe heuristic method (complete brainrot)

Answer 36

We don’t gather/measure all the data (1) about vehicle speeds (1). We scan for the data most likely to help us (1) and make a judgement based on experience (1).