Which data type would store the value 3.14?

REAL. It has a fractional part.

Which data type is best for a single letter such as a grade 'B'?

CHAR. CHAR holds one character.

Which data type should be used for a telephone number?

STRING. No calculations are done with it, and a leading zero must be kept.

a named value that cannot change while the program runs. Such as the number of days in a week.

What does DECLARE Score : INTEGER do?

creates a variable called Score that holds whole numbers. It names the variable and gives its data type.

Variables, constants and data types · Cambridge IGCSE Computer Science (9

In plain words

A program has to remember things as it runs: a score, a name, whether the game is over. Each is kept in a named place in memory. If the value may change, the place is a variable. If it must never change, it is a constant.

Every one has a data type, which says what kind of value it holds and so what can be done with it.

6 things to know

A variable is a named store in memory whose value can change while the program runs. A constant is a named store whose value cannot change while the program runs.
Declaring a variable: DECLARE Age : INTEGER. Declaring a constant: CONSTANT TaxRate ← 0.2.
INTEGER: a whole number, such as 17 or −3. REAL: a number with a fractional part, such as 3.75.
CHAR: a single character, such as 'M'. STRING: a sequence of characters, such as "Hello". BOOLEAN: TRUE or FALSE.
Assignment gives a variable a value: Age ← 16. INPUT Name reads a value from the user. OUTPUT "Hello ", Name displays text and a value.
Give every variable and constant a meaningful name, such as TotalCost, not T.

Worked example

A program stores a person's name, age, height in metres, and whether they hold a ticket. Choose a data type for each.

The name is a sequence of characters: STRING.
The age is a whole number: INTEGER.
The height, such as 1.62, has a fractional part: REAL.
Holding a ticket is yes or no: BOOLEAN.

Tips and tricks

A phone number is a STRING, not an INTEGER. No arithmetic is done with it, and as a number it would lose its leading zero.
A constant makes a program easier to maintain: if the value changes, it is changed in one place only.

6 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Variables, constants and data types: 6 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

Which data type would store the value 3.14?
- INTEGER
- REAL (the answer)
- CHAR
- BOOLEAN
It has a fractional part.
Which data type stores only TRUE or FALSE?
- STRING
- CHAR
- BOOLEAN (the answer)
- INTEGER
Two possible values.
Which data type is best for a single letter such as a grade 'B'?
- CHAR (the answer)
- STRING
- REAL
- BOOLEAN
CHAR holds one character.
Which data type should be used for a telephone number?
- INTEGER
- REAL
- STRING (the answer)
- BOOLEAN
No calculations are done with it, and a leading zero must be kept.
What is a constant?
- a variable that is never used
- a named value that cannot change while the program runs (the answer)
- a number that is very large
- a kind of loop
Such as the number of days in a week.
What does DECLARE Score : INTEGER do?
- outputs the score
- creates a variable called Score that holds whole numbers (the answer)
- sets Score to zero
- inputs a number
It names the variable and gives its data type.

6 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

2 questions, 6 marks. Write your answers on paper, then check them.

Variables, constants and data types

Cambridge IGCSE Computer Science (9–1) 0984 · 6 marks · papermunch.org

Name ______________________________ Date ______________

Describe the difference between a variable and a constant.[2]
Show answerHide answer
The value of a variable can change while the program is running. The value of a constant cannot.
I got this one
State the most suitable data type for each of these: the price of a book, the number of books in stock, the title of the book, whether the book is on loan.[4]
Show answerHide answer
Price: REAL. Number in stock: INTEGER. Title: STRING. On loan: BOOLEAN.
I got this one

Answers: Variables, constants and data types

1. The value of a variable can change while the program is running. The value of a constant cannot.
2. Price: REAL. Number in stock: INTEGER. Title: STRING. On loan: BOOLEAN.