Variables, Data Types & Operators (Years 6–10) — Computer Science

How programs remember values in named variables, the main data types, and the operators that work on them.

Every program you have ever used — a game, a calculator, a messaging app — is really just moving values around and doing sums with them. A variable is the program's way of remembering a value and giving it a name, so it can fetch it back later. Master variables and you have the vocabulary that the rest of programming is built from.

Why this matters: You cannot write a single useful program without storing data. Scores, passwords, prices, the number of lives you have left — all of it lives inside variables. Choosing the right data type and the right operator is the difference between code that works and code that crashes.

A variable is a named box holding one value at a time.

Variables: named boxes

Assignment works out the right side first, then drops the answer in the box.

Think of a variable as a labelled box in a warehouse. The name is written on the outside; the value is what sits inside. You put a value in using assignment, written with an equals sign that means "becomes":

score = 7
name  = "Ava"
score = score + 1

That last line trips people up. It does not mean "score equals score plus one" as a fact — it means "work out the right-hand side, then drop the answer back in the box". So score goes from 7 to 8.

Data types: what kind of value?

Each data type is a different bin: a value goes in the one that fits it.

Every value has a type, and the type decides what you can do with it. You can add two numbers, but adding two names makes no sense.

Type	Holds	Example
Integer	Whole number	42
Real (float)	Number with a decimal	3.14
String	Text in quotes	"hello"
Boolean	True or False only	True
Character	A single symbol	'q'

Operators: doing things with values

DIV keeps the whole part of a division; MOD keeps the remainder.

Arithmetic operators do maths: + - * /. Two special ones matter for exams: DIV gives the whole-number part of a division, and MOD gives the remainder. So 17 DIV 5 is 3 and 17 MOD 5 is 2.

Comparison operators ask a yes/no question and give back a Boolean: == (equal), != (not equal), <, >, <=, >=.

A comparison always answers with a Boolean: True or False.

Worked trace.
a = 5 → box a holds 5
b = 2 → box b holds 2
total = a * b → 5 × 2 = 10, so total holds 10
rem = 5 MOD 2 → 5 ÷ 2 leaves remainder 1, so rem holds 1
check = total > 8 → 10 > 8 is true, so check holds True

Common mistake: confusing = (assignment, "put this value in the box") with == (comparison, "are these equal?"). Writing if score = 10 when you mean if score == 10 is one of the most common beginner errors.

Give your variables honest names. numberOfLives tells the reader — and future you — exactly what the box holds; x tells them nothing.