Variables and constants

Question 1

What are variables and constants used for?

Answer 1

To store values in algorithms and programs

Question 2

Use of identifiers (2), long and short versions, and limitations (2)

Answer 2

A name given to a variable or constant

Identifiers describe the data being stored

• short identifiers are easier to spell correctly each time they are used
• long identifiers can be used if they are more descriptive (e.g. firstName)

They can’t be the same as reserved words such as print or while
They must be consistent throughout the program

Question 3

Difference between variables and constants

Answer 3

Variables can change while a program is running

Constants must not change while a program is running

Question 4

assignment statements

Answer 4

Variables are assigned in assignment statements using the = symbol

They can be changed while the program is running, e.g. variable = variable * 2

Question 5

Constants

Answer 5

They are assigned using:

const (name) = (value)
const Pi = 3.142

They are used in calculations

Question 6

Camel case and snake case

Answer 6

Ways to format identifiers

In camel case, lower and upper case characters are used
The first word can be lower case (or not):
variableName
VariableName
FirstName
pricePerKilo
PricePerKilo

In snake case words are linked with an underscore:
first_name
price_per_kilo

Question 7

Assignments

Answer 7

The association of a piece of data with a variable or constant

Often done as an input

Variables can be output to the user and will print the value rather than the identifier:
print(name) doesn’t output the word ‘name’

Question 8

Identify the variables that are used in this algorithm and state the purpose of each. [6]

length = input ("Enter the length of the rectangle.")
width = input ("Enter the width of the rectangle.")

area = length * width

print(area)

Answer 8

The variables are:
length, width, and area

length and width store values that are input by the user, and area stores the result of multiplying the length by the width

Question 9

A student is writing an algorithm that allows a user to input their marks for five tests and then calculate the average mark.

List suitable variables that can be used in the algorithm. [1]

Answer 9

result1, result2, “, “, “, average