← IGCSE Computer Science Paper 2

Assigned value must match the variable's data type

An error when a value assigned to a variable has a different data type from the one it was declared with, such as storing a name in an INTEGER variable.

Part of: IGCSE Computer Science 0478 — 8.1a Data Types and Variables — Module 9

Understanding Assigned value must match the variable's data type in IGCSE Computer Science Paper 2

What it does: STRING values are written in double quotes, so "Ali" matches the STRING variable Name. Age was declared as INTEGER, so it can only hold whole numbers. "Ali" is a STRING, which causes a type mismatch. 42 is an INTEGER literal and the variable is declared as INTEGER, so the types match. A CHAR holds exactly one character in single quotes. "Ali" is a STRING, so the types do not match.

Common mistakes: Age was declared as INTEGER, so it can only hold whole numbers. The text "Ali" is a STRING, which causes a type mismatch. It should be a whole number such as Age ← Age + 1. Name is assigned the text "Ali", so it must be declared as STRING. An INTEGER variable cannot hold text. It should be DECLARE Name : STRING.

Class: _____________________ · Name: _____________________ · Date: _________

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This module's key terms are also in a printable crossword (Modules 317–326) and word search (Modules 317–336).

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Learning

Duo

DECLARE Age : INTEGER Age ← "Ali"

Valid: Age can hold any value you assign to itType mismatch: a STRING cannot be stored in an INTEGER variable

Matches

DECLARE Score : INTEGER Score ← "Ali"

↓

Type mismatch: text is assigned to an INTEGER variable. Score should be given a whole number such as 45.

Applying

Meanings

Term

type mismatch

Meaning

An error when a value assigned to a variable has a different data type from the one it was declared with, such as storing a name in an INTEGER variable.

Practice

DECLARE Age : INTEGER

Testing

Gaps

DECLARE Age :

Check Answer

Spots

2Age ← 15

3Age ← "Ali"

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Quick Questions

1. DECLARE Age : INTEGER Age ← "Ali"

A. Valid: Age can hold any value you assign to it

B. Type mismatch: a STRING cannot be stored in an INTEGER variable ✓

Age was declared as INTEGER, so it can only hold whole numbers. "Ali" is a STRING, which causes a type mismatch.

2. Which assignment is correct for DECLARE Name : STRING?

A. Name ← Ali

B. Name ← "Ali" ✓

STRING literals must be written inside double quotes. Without quotes, Ali looks like an identifier, not text.

3. Which assignment is correct for DECLARE Grade : CHAR?

A. Grade ← 'A' ✓

B. Grade ← "A"

In Cambridge pseudocode a CHAR literal uses single quotes. Double quotes mark a STRING.

4. DECLARE Score : INTEGER Score ← 42 Is this assignment valid?

A. Yes: 42 is a whole number, so it matches INTEGER ✓

B. No: numbers cannot be stored in variables

42 is an INTEGER literal and the variable is declared as INTEGER, so the types match.

5. DECLARE Initial : CHAR Initial ← "Ali" What is the problem?

A. A STRING of several characters is assigned to a CHAR variable ✓

B. The variable name Initial is not allowed

A CHAR holds exactly one character in single quotes. "Ali" is a STRING, so the types do not match.

Match the Pairs

DECLARE Age : INTEGER Age ← "Ali" → A type mismatch: the text "Ali" cannot be stored in an INTEGER variable

DECLARE Grade : CHAR Grade ← 'B' → A correct assignment: a single character in single quotes matches the CHAR type

A STRING variable must be given text inside double quotes → DECLARE Name : STRING Name ← "Ali"

A CHAR variable must be given a single character inside single quotes → DECLARE Initial : CHAR Initial ← 'A'

DECLARE Score : INTEGER Score ← "Ali" → Type mismatch: text is assigned to an INTEGER variable. Score should be given a whole number such as 45.

DECLARE Letter : CHAR Letter ← "A" → A CHAR value needs single quotes, not double quotes. It should be Letter ← 'A'.

Key Term

type mismatch

An error when a value assigned to a variable has a different data type from the one it was declared with, such as storing a name in an INTEGER variable.

Fill in the Blanks

1. DECLARE Age : INTEGER Age ← 15

Hint: Type the data type that matches the whole number 15 being assigned.

2. DECLARE Name : STRING Name ← "Ali"

Hint: Type the data type that matches text written in double quotes.

3. DECLARE Grade : CHAR Grade ← 'A'

Hint: Type the data type that matches a single character in single quotes.

4. DECLARE Town : STRING Town ← "Leeds"

Hint: Type the assignment operator that stores a value in the variable.

5. DECLARE Initial : CHAR Initial ← 'K'

Hint: Type the keyword that creates a variable with a fixed data type.

Spot the Error

Question 1

A DECLARE Age : INTEGER

B Age ← 15

C Age ← "Ali"

D OUTPUT Age

Line C — Age was declared as INTEGER, so it can only hold whole numbers. The text "Ali" is a STRING, which causes a type mismatch. It should be a whole number such as Age ← Age + 1.

Question 2

A DECLARE Name : INTEGER

B Name ← "Ali"

C OUTPUT Name

Line A — Name is assigned the text "Ali", so it must be declared as STRING. An INTEGER variable cannot hold text. It should be DECLARE Name : STRING.

Question 3

A DECLARE Grade : BOOLEAN

B Grade ← 'B'

C OUTPUT Grade

Line A — Grade stores the single character 'B', so it must be declared as CHAR. A BOOLEAN variable can only hold TRUE or FALSE. It should be DECLARE Grade : CHAR.

Question 4

A DECLARE City : STRING

B DECLARE Age : INTEGER

C City ← Leeds

D Age ← 14

Line C — A STRING value needs double quotes. Without them, Leeds looks like a variable name, not text. It should be City ← "Leeds".

Question 5

A DECLARE Initial : CHAR

B DECLARE Name : STRING

C Initial ← "A"

D Name ← "Ali"

Line C — A CHAR value must be written in single quotes. Double quotes make it a STRING literal, which is a type mismatch. It should be Initial ← 'A'.

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