Cambridge IGCSE 0478 · Topic 8 · 8.1a

Variables, Data Types
& Constants

Data Types · Variables vs Constants · Casting · Sequence

CSZoneCambridge IGCSE Computer Science 0478

Data Types

Choosing the Right Type

Data Type	Description	Example
INTEGER	Whole number	42, -7, 0
REAL	Number with decimal	3.14, -0.5
STRING	Text / sequence of characters	"Hello", "AB12"
BOOLEAN	TRUE or FALSE only	TRUE, FALSE
CHAR	Single character	'A', '3'

Choosing the right data type matters — storing an age as REAL wastes memory; storing a postcode as INTEGER is wrong

Variables vs Constants

Storing Values in Programs

Variable: a named storage location whose value can change during program execution. Declared with a name and data type.

Constant: a named storage location whose value is set once and cannot change during execution. Used for fixed values like PI or VAT_RATE.

DECLARE score : INTEGER // variable
CONSTANT PI ← 3.14159 // constant
score ← 85 // assign value
OUTPUT score * PI // use both

Sequence & Type Casting

Order of Execution & Conversions

Sequence: instructions execute one after another in the order written. No jumps unless a control structure (IF, loop) is used. The most basic programming construct.

// Type casting functions (Cambridge 0478)
INT("42") → 42 // string to integer
REAL("3.14") → 3.14 // string to real
STR(100) → "100" // integer to string

// Useful for combining INPUT (always string) with arithmetic
INPUT ageStr
age ← INT(ageStr)
OUTPUT age + 1

Exam Practice

Have a go at this question

Cambridge IGCSE 0478 style

A programmer needs to store a student's name, age, height (in metres), and whether they are enrolled. State the most appropriate data type for each piece of data and give a reason for one of your choices.

5 marks

Name: STRING [1]; Age: INTEGER [1]; Height: REAL [1]; Enrolled: BOOLEAN [1]. Reason: Height is REAL because it requires a decimal point (e.g. 1.72m) and INTEGER would lose the fractional part [1].

Key Takeaways

What to Remember

5 data types: INTEGER, REAL, STRING, BOOLEAN, CHAR — choose based on the data being stored

Variable: value can change; Constant: value fixed throughout the program (e.g. PI, VAT_RATE)

Sequence: instructions run top to bottom in order — the default execution model

Type casting: INT(), REAL(), STR() convert between types — INPUT always returns a string in Cambridge 0478