The five data types

Every value your program stores has a data type. AQA expects you to know these five:

• Integer — a whole number, positive or negative, with no decimal part (e.g. -7, 42).
• Real (also called float) — a number with a decimal part (e.g. 3.14, -0.5).
• Boolean — one of only two values: True or False.
• Character — a single letter, digit or symbol (e.g. 'A', '?').
• String — a sequence of characters (e.g. "Hello").

Why it matters: choosing the right type saves memory and prevents errors — e.g. store a person's age as an integer, a price as a real, and a yes/no flag as a Boolean.

Which data type?

Variables vs constants

Both are named stores for data, but they differ in whether the value can change:

• A variable holds a value that can change while the program runs (e.g. a running score).
• A constant holds a value that is set once and never changes while the program runs (e.g. PI ← 3.142 or VAT ← 0.20).

Remember: using a constant makes code easier to read and safer — you can't accidentally overwrite a value that's meant to stay fixed.

Sequence, selection & iteration

Every program is built from just three constructs:

• Sequence — statements run one after another, top to bottom.
• Selection — a choice is made with a condition (IF … THEN … ELSE).
• Iteration — code repeats. A count-controlled loop (FOR) runs a set number of times; a condition-controlled loop (WHILE) repeats until a condition is met.

Key contrast: a FOR loop is count-controlled (you know how many times up front); a WHILE loop is condition-controlled (it repeats while a condition stays true).

Which construct is it?

Tap a description, then tap the construct it belongs to.

Arithmetic, relational & Boolean operators

AQA groups operators into three families:

• Arithmetic: + - * /, plus MOD (remainder), DIV (integer division) and ^ (exponent / "to the power of").
• Relational: =, <, >, <=, >= and != (not equal) — they compare two values and give a Boolean.
• Boolean: AND, OR, NOT — combine or reverse conditions.

Tip: MOD gives the left-over; DIV gives the whole number of times. MOD is handy for testing "is a number even?" — n MOD 2 = 0 means even.

Your turn — MOD

Your turn — DIV

Arrays (1D and 2D)

An array stores many values under one name, each reached by an index. In AQA pseudocode arrays are zero-indexed — the first item is at index 0.

Watch out: because arrays start at 0, an array with 5 items has indexes 0 to 4 — there is no index 5.

Your turn — array index

Procedures & functions

A subroutine is a named block of code you can call whenever you need it. AQA distinguishes two kinds:

• A function returns a value back to the code that called it (e.g. a function that returns the square of a number).
• A procedure carries out a task but does not return a value (e.g. a procedure that just prints a message).

The key difference: a function returns a value you can use in an expression; a procedure just does its job with no value handed back.

Function or procedure?

Strings & text files

String handling operations you must know:

• LENGTH — how many characters, e.g. LENGTH("cat") = 3.
• SUBSTRING / indexing — pull out part of a string by position.
• Concatenation — join two strings together, e.g. "Hello" + " world".
• .UPPER / .LOWER — convert a string to upper- or lower-case.

File handling follows four steps: open a text file, read from or write to it, then close it.

Remember: always close a file when you're finished — leaving it open can lose data or lock the file.

Match term to meaning

Tap a description on the left, then its matching term on the right.

SQL basics & validation

SQL (Structured Query Language) fetches data from a database table. The basic query is SELECT … FROM … WHERE:

Validation checks that input is sensible and allowable before the program uses it. Common checks:

• Range check — is the value between allowed limits? (e.g. age 0–120)
• Length check — is it the right number of characters?
• Presence check — has something actually been entered?
• Type check — is it the right data type? (e.g. a number, not text)

Don't confuse: validation checks input is reasonable/allowable; verification checks input was entered correctly (e.g. typing a password twice to confirm it matches).

Count or condition?

What is validation?

The big ideas to know

You've covered all of AQA 3.2 — data types, constructs, operators, arrays, subroutines, strings, files, SQL and validation. Press Finish to see your score.