← IGCSE Computer Science Paper 2

BOOLEAN data type

A data type with only two possible values, TRUE or FALSE, written without quotes. Used for yes/no information, e.g. DECLARE GameOver : BOOLEAN

Part of: IGCSE Computer Science 0478 — 8.1a Data Types and Variables — Module 18

Understanding BOOLEAN data type in IGCSE Computer Science Paper 2

What it does: Yes/no information is stored in a BOOLEAN variable, which can only be TRUE (yes) or FALSE (no). Writing FALSE with no quotes assigns the BOOLEAN value. Quotes would make it a STRING instead. BOOLEAN is the Cambridge pseudocode data type for yes/no information. YESNO is not a data type.

Common mistakes: FALSE is a keyword, not a string. With quotes it becomes a STRING, which cannot be stored in a BOOLEAN. It should be GameOver ← FALSE. A BOOLEAN variable can only hold TRUE or FALSE. The number 1 is an INTEGER, so it must be Passed ← TRUE.

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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

Which declaration correctly creates a variable that stores yes/no information?

DECLARE GameOver : YESNODECLARE GameOver : BOOLEAN

Matches

GameOver ← "TRUE"

↓

TRUE is in quotes, so it is a STRING and not a BOOLEAN value. It should be GameOver ← TRUE

Applying

Meanings

Term

BOOLEAN

Meaning

A data type with only two possible values, TRUE or FALSE, written without quotes. Used for yes/no information, e.g. DECLARE GameOver : BOOLEAN

Practice

DECLARE GameOver : BOOLEAN

Testing

Gaps

DECLARE GameOver :

Check Answer

Spots

1DECLARE GameOver : BOOLEAN

2GameOver ← "FALSE"

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Quick Questions

1. Which declaration correctly creates a variable that stores yes/no information?

A. DECLARE GameOver : YESNO

B. DECLARE GameOver : BOOLEAN ✓

BOOLEAN is the Cambridge pseudocode data type for yes/no information. YESNO is not a data type.

2. How many different values can a BOOLEAN variable hold?

A. Two: TRUE and FALSE ✓

B. Any whole number

A BOOLEAN can only ever be TRUE or FALSE. Whole numbers are stored in INTEGER variables.

3. Which line assigns a BOOLEAN value correctly?

A. GameOver ← TRUE ✓

B. GameOver ← "TRUE"

TRUE and FALSE are keywords, so they are written without quotes. With quotes, "TRUE" is just a STRING.

4. Which statement about TRUE and FALSE is correct?

A. They must always be written in quotes

B. They are keywords, not strings ✓

TRUE and FALSE are BOOLEAN literals. Quotes would turn them into text and cause a data type mismatch.

5. Which piece of information is best stored in a BOOLEAN variable?

A. Whether the player has won (yes or no) ✓

B. The player's full name

A name is a STRING. Only yes/no information, such as won or not won, suits a BOOLEAN.

Match the Pairs

DECLARE GameOver : BOOLEAN → Creates a variable called GameOver that can only store TRUE or FALSE

GameOver ← TRUE → Stores the BOOLEAN value TRUE in GameOver, for example to show the game has ended

A BOOLEAN variable can hold yes/no information, such as whether a player has finished the level → DECLARE LevelComplete : BOOLEAN

TRUE and FALSE are keywords, so they are written without quotes when assigned → GameOver ← FALSE

GameOver ← "TRUE" → TRUE is in quotes, so it is a STRING and not a BOOLEAN value. It should be GameOver ← TRUE

GameOver ← YES → YES is not a BOOLEAN value. A BOOLEAN can only be TRUE or FALSE, so use GameOver ← TRUE

Key Term

BOOLEAN

A data type with only two possible values, TRUE or FALSE, written without quotes. Used for yes/no information, e.g. DECLARE GameOver : BOOLEAN

Fill in the Blanks

1. DECLARE GameOver : BOOLEAN

Hint: Type the data type used for yes/no information that can only be one of two values.

2. GameOver ← FALSE

Hint: Type the Boolean keyword meaning the game has not ended yet. It is a keyword, so no quotes.

3. DECLARE IsRaining : BOOLEAN

Hint: Type the keyword that creates a new variable before it is used.

4. IF Lives = 0 THEN GameOver ← TRUE ENDIF

Hint: Type the Boolean keyword meaning yes, written without quotes.

5. DECLARE LoggedIn : BOOLEAN LoggedIn ← TRUE OUTPUT LoggedIn

Hint: Type the name of the Boolean variable whose value should be displayed.

Spot the Error

Question 1

A DECLARE GameOver : BOOLEAN

B GameOver ← "FALSE"

C IF GameOver = TRUE THEN

D OUTPUT "Game over"

E ENDIF

Line B — FALSE is a keyword, not a string. With quotes it becomes a STRING, which cannot be stored in a BOOLEAN. It should be GameOver ← FALSE.

Question 2

A DECLARE Passed : BOOLEAN

B DECLARE Score : INTEGER

C Score ← 72

D Passed ← 1

E OUTPUT Passed

Line D — A BOOLEAN variable can only hold TRUE or FALSE. The number 1 is an INTEGER, so it must be Passed ← TRUE.

Question 3

A DECLARE IsOpen : BOOLEAN

B IsOpen ← TRUE

C IF IsOpen = "TRUE" THEN

D OUTPUT "Open"

E ENDIF

Line C — TRUE must be written without quotes. "TRUE" is a string, not a BOOLEAN value. It should be IF IsOpen = TRUE THEN.

Question 4

A DECLARE Lives : INTEGER

B DECLARE Alive : BOOLEAN

C Alive ← Lives

D OUTPUT Alive

Line C — Lives is an INTEGER, so it cannot be assigned to a BOOLEAN variable. Use a comparison that gives TRUE or FALSE, such as Alive ← Lives > 0.

Question 5

A DECLARE Done : BOOLEAN

B Done = FALSE

C OUTPUT Done

Line B — Assignment uses the ← operator, not =. A line starting Done = FALSE is a comparison, not an assignment. It should be Done ← FALSE.

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