Data Structures

Question 1

What is a variable?

Answer 1

An identifier/address in memory for a value stored in RAM

Extra info:
- use direct addressing type
- used to manipulate data behind the scenes
- some languages need explicit variable declarations - define variable name + type

Question 2

What is a constant?

Answer 2

Like a variable but you can’t change the value stored in it - immutable

Question 3

What is an array?

Answer 3

• A set of data items of the same type grouped together using a single identifier
• they are zero indexed - the first value is index zero
• values are identified by variable name + subscript - Eg. Arr_name[4]

Question 4

What are the features of an array?

Answer 4

• they have a fixed size, defined at the start
• they can’t expand or shrink
• all data must be of the same data type

Question 5

What is a 2D array?

Answer 5

• it’s an array inside an array - can be visualised as a table

Eg. [[a,b],[c,d]]
To choose b:
- pseudocode - arr[0,2]
- python - arr[0][2]

Question 6

what is a 3D array?

Answer 6

• its an array with arrays inside it with arrays inside the sub-arrays
• can be visualised as a multi page spreadsheet
• eg. [[[a,b],[c,d]],[[e,f],[g,h]]]
  to select e:
• pseudocode - arr[1,0,0]
• python - arr[1][0][0]

Question 7

why would you use arrays of multiple dimensions?

Answer 7

do this to avoid using multiple arrays - you are the programmer so won’t forget what each array stands for

Question 8

what is a record?

Answer 8

• its essentially a row in a table
• data is organised via attributes/fields (columns) which hold one item of data - the primary key and/or secondary keys can be used to order multiple records
• more user-friendly than a list/array because you can identify data by attribute

Question 9

how do you declare a record in pseudocode?
(eg define record studentType with fields ID, firstname, surname, dateOfBirth, class)

how do you identify a field in a record

Answer 9

studentType = record
    integer ID
    string firstname
    string surname
    date dateOfBirth
    string class
end record

variable must be declared first like this:
~~~

<variable> : <variableType>
<recordname>.<fieldname>
~~~
</fieldname></recordname></variableType></variable>

Question 10

what is a tuple?

Answer 10

• an ordered set of elements of any data type
• elements do not have to be of the same data type
• it is immutable - elements can’t be changed, added or deleted dynamically

Question 11

how do you define a tuple in python and refer to a value in it?

Answer 11

use parenthesis

pupil = ("John", 78, "a") 

name = pupil[0]

Question 12

what is a list?

Answer 12

• its a dynamic data type consisting of a number of ordered items where the same item may occur more than once
• they are dynamic - items can be added, removed and edited
• items can be of different data types

Question 13

what are some common operations on a list?

Answer 13

• isEmpty() - test for empty list
• append(item) - add an item to the end of the list
• remove(item) - remove first occurence of an item from the list
• search(item) - search for an item in the list
• length() - return the number of items in the list
• index(item) - return the position of