Variables, Data Types & Arithmetic

Variables, Data Types & Arithmetic

What is a variable?

Every useful program needs to store data — values typed by the user, results of calculations, or information the program needs to remember. A variable is a named storage location in the computer's memory that holds a single item of data.

Think of a variable like a labelled box: the label is the variable's name, and whatever is inside the box is its current value. When you put something new in the box, the old contents are permanently replaced — a variable can only hold one value at a time.

Variables must be given a meaningful name that describes what they store. A variable called score is immediately understandable; a variable called x is not. Meaningful names make code easier to read, maintain, and debug.

Declaring a variable

Before a variable can be used in a program, it must be declared — this reserves a space in memory and tells the translator what kind of data it will hold. In SQA reference language the syntax is:

DECLARE variableName AS DATATYPE INITIALLY startingValue

Examples:

DECLARE score AS INTEGER INITIALLY 0
DECLARE playerName AS STRING INITIALLY ""
DECLARE average AS REAL INITIALLY 0.0
DECLARE firstLetter AS CHARACTER INITIALLY ""
DECLARE gameOver AS BOOLEAN INITIALLY FALSE

Note that Python does not require variable declarations — it works out the type automatically when the variable is first assigned a value. This is called dynamic typing. In the exam, always use SQA reference language syntax.

The five data types

A data type defines what kind of data a variable can store and what operations can be performed on it. There are five data types at N5:

1. Character
Stores a single letter, digit, or symbol. Internally the computer stores the ASCII code for that symbol.

DECLARE firstInitial AS CHARACTER INITIALLY ""
SET firstInitial TO "R"

Examples of character values: "A", "7", "@", "!"

2. String
Stores a sequence of characters — essentially any piece of text. A phone number is stored as a string (not an integer) because it may start with 0, and you never do arithmetic with it.

DECLARE username AS STRING INITIALLY ""
SET username TO "coolcoder99"

Examples: "Edinburgh", "L3tme!n#@", "0131 252 5000"

3. Integer
Stores a positive or negative whole number. No decimal point is possible.

DECLARE score AS INTEGER INITIALLY 0
SET score TO 42

Examples: 0, -6, 1000, -999. Key point: integers never appear in double quotes in code — quotes are for characters and strings only.

4. Real
Stores a positive or negative number that can include a decimal point. In other languages this may be called float or single, but in the N5 exam you must always use the term real.

DECLARE average AS REAL INITIALLY 0.0
SET average TO 7.35

Examples: 3.14, -0.5, 186.332

5. Boolean
Can only store two values: TRUE or FALSE. Booleans are commonly used as flags — to track whether something has happened yet.

DECLARE gameOver AS BOOLEAN INITIALLY FALSE
IF score > 100 THEN
    SET gameOver TO TRUE
END IF

Booleans connect directly to how all digital computers work at hardware level — everything ultimately comes down to 1s and 0s, true or false.

Choosing the right data type

Choosing the wrong data type is one of the most common mistakes at N5. Use this approach:

• Is it a whole number you'll do arithmetic with? → Integer
• Is it a number with a decimal point? → Real
• Is it text, or a number you won't calculate with (like a postcode or phone number)? → String
• Is it a single letter or symbol? → Character
• Can it only ever be true or false? → Boolean

Assignment

Once a variable is declared, you store data in it using assignment:

SET variableName TO value

The computer reads the right-hand side first, works out the value, then stores the result in the variable on the left.

SET score TO 0
SET playerName TO "Maya"
SET average TO score / 10

Arithmetic operators

When working with integers and real numbers, you can use arithmetic operators to perform calculations. The five operators at N5 are:

Arithmetic operators are processed by the ALU (Arithmetic Logic Unit) inside the processor. The computer always evaluates the right-hand side of an assignment before storing the result.

SET area TO length * breadth
SET total TO price + (price * 0.2)

BODMAS — operator precedence

When an expression contains more than one operator, the order in which they are calculated matters. Python and SQA reference language follow the same mathematical rule: BODMAS.

This means multiplication and division are always performed before addition and subtraction, unless brackets override the order.

Common BODMAS trap:

SET average TO num1 + num2 + num3 / 3   ← WRONG (divides num3 by 3 first)
SET average TO (num1 + num2 + num3) / 3  ← CORRECT (brackets force the addition first)

String concatenation

Concatenation means joining two or more strings together to form a longer string. At N5, the + operator is used for concatenation:

DECLARE firstName AS STRING INITIALLY ""
DECLARE surname AS STRING INITIALLY ""
SET firstName TO "Rohan"
SET surname TO "Singh"
SEND "Hello " + firstName + " " + surname + "!" TO DISPLAY

Output: Hello Rohan Singh!

Concatenation is also used to include variable values in output messages:

SEND "Your score is " + score + " out of 100." TO DISPLAY

At N5, the + operator is used to join each part of the output message in SEND statements.