← IGCSE Computer Science Paper 2

Choosing a suitable data type for a value

Pick INTEGER, REAL, CHAR, STRING or BOOLEAN by what the value is and what you do with it, then justify with 'because'. Eg price is REAL because it has pence.

Part of: IGCSE Computer Science 0478 — 8.1a Data Types and Variables — Module 22

Understanding Choosing a suitable data type for a value in IGCSE Computer Science Paper 2

What it does: A whole number used in calculations is stored as INTEGER, and the 'because' reason justifies the choice. One character only means CHAR is the suitable type for an initial. Prices usually include pence, so they need REAL. INTEGER would lose the decimal part. CHAR holds exactly one character. An address is many characters of text (and includes numbers and spaces), so it is a STRING. A fact with only two possible values points to BOOLEAN. It is simpler and safer than storing text. A mark needs a reason linked to the value. Say why the type fits, for example that the price can have pence, rather than just repeating the data name.

Common mistakes: Whether someone is a member has only two possible values (yes or no), so it should be BOOLEAN, not STRING. Correct line: DECLARE IsMember : BOOLEAN. A price has pence, so it needs decimal places. It must be REAL because INTEGER only stores whole numbers. Correct line: DECLARE Price : REAL.

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This module's key terms are also in a printable crossword (Modules 327–336) and word search (Modules 317–336).

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Learning

Duo

A program stores a student's age in whole years. Which data type and reason is best?

INTEGER because age in whole years is a whole numberREAL because age is a number

Matches

DECLARE Address : INTEGER

↓

An address is text made of letters, numbers and spaces and is never used in calculations, so it should be STRING, not INTEGER

Applying

Meanings

Term

data type

Meaning

Pick INTEGER, REAL, CHAR, STRING or BOOLEAN by what the value is and what you do with it, then justify with 'because'. Eg price is REAL because it has pence.

Practice

DECLARE Age : INTEGER // whole number of years

Testing

Gaps

DECLARE Age :

Check Answer

Spots

3DECLARE Initial : CHAR

4DECLARE IsMember : STRING

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Quick Questions

1. A program stores a student's age in whole years. Which data type and reason is best?

A. INTEGER because age in whole years is a whole number ✓

B. REAL because age is a number

Whole-number values such as an age in years use INTEGER. REAL is only needed when the value can have a decimal part.

2. A program stores the price of a notebook, such as 4.75. Which data type and reason is best?

A. REAL because the price has pence (a decimal part) ✓

B. INTEGER because a price is a number

Prices usually include pence, so they need REAL. INTEGER would lose the decimal part.

3. A program stores a member's initial, for example 'J'. Which data type is best?

A. STRING because it is a name

B. CHAR because it is a single character ✓

One single character is CHAR. STRING is for text of any length, but the initial is only one character.

4. A program stores an address such as "12 High Street". Which data type is best?

A. CHAR because it is one piece of data

B. STRING because it is several characters of text ✓

CHAR holds exactly one character. An address is many characters of text (and includes numbers and spaces), so it is a STRING.

5. A program records whether a customer is a member: either yes or no. Which data type is best?

A. BOOLEAN because it has only two possible values (TRUE or FALSE) ✓

B. STRING because it could be typed as the word yes or no

A fact with only two possible values points to BOOLEAN. It is simpler and safer than storing text.

Match the Pairs

DECLARE Price : REAL → Price holds a money amount with pence, so it needs a number type that can store decimal places

DECLARE IsMember : BOOLEAN → IsMember holds a two-valued fact that is either TRUE or FALSE, so BOOLEAN is chosen

An age is a whole number that is used in calculations, so it is INTEGER because it has no decimal part → DECLARE Age : INTEGER

A single letter such as a first initial is stored as CHAR because it is exactly one character → DECLARE Initial : CHAR

DECLARE Address : INTEGER → An address is text made of letters, numbers and spaces and is never used in calculations, so it should be STRING, not INTEGER

DECLARE Price : INTEGER → A price has pence, so INTEGER would lose the decimal part. It should be REAL because it can hold decimals

Key Term

data type

Pick INTEGER, REAL, CHAR, STRING or BOOLEAN by what the value is and what you do with it, then justify with 'because'. Eg price is REAL because it has pence.

Fill in the Blanks

1. // a person's age in whole years DECLARE Age : INTEGER

Hint: Type the data type for a whole number with no decimal part.

2. // a price such as 2.50 with pence DECLARE Price : REAL

Hint: Type the data type for a number that can have a decimal part.

3. // the first letter of a name DECLARE Initial : CHAR

Hint: Type the data type for exactly one single character.

4. // is the customer a member? TRUE or FALSE DECLARE IsMember : BOOLEAN

Hint: Type the data type for a two-valued fact that is either true or false.

5. // house number, street and town DECLARE Address : STRING

Hint: Type the data type for text made of several characters, including digits and letters.

Spot the Error

Question 1

A DECLARE Age : INTEGER

B DECLARE Price : REAL

C DECLARE Initial : CHAR

D DECLARE IsMember : STRING

Line D — Whether someone is a member has only two possible values (yes or no), so it should be BOOLEAN, not STRING. Correct line: DECLARE IsMember : BOOLEAN.

Question 2

A DECLARE Price : INTEGER

B Price ← 4.75

C OUTPUT Price

Line A — A price has pence, so it needs decimal places. It must be REAL because INTEGER only stores whole numbers. Correct line: DECLARE Price : REAL.

Question 3

A DECLARE Initial : CHAR

B Initial ← 'Kim'

C OUTPUT Initial

Line B — An initial is one character, so a CHAR variable can only hold a single character such as 'K'. 'Kim' is three characters and belongs in a STRING.

Question 4

A DECLARE Age : INTEGER

B Age ← 15

C DECLARE IsMember : BOOLEAN

D IsMember ← "TRUE"

Line D — With quote marks, "TRUE" is a STRING, not a BOOLEAN. A BOOLEAN value is written without quotes. Correct line: IsMember ← TRUE.

Question 5

A DECLARE Price : REAL

B DECLARE Qty : BOOLEAN

C DECLARE Total : REAL

D Total ← Price * Qty

Line B — A quantity is a whole number that is used in a calculation, so it should be INTEGER. BOOLEAN is only for two-valued facts such as TRUE or FALSE. Correct line: DECLARE Qty : INTEGER.

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