Data Structures is a core part of A-Level Computer Science. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
BinaryBase-2 representation using only 0s and 1s.
HexadecimalBase-16, a shorthand for binary (0–9, A–F).
Bits & bytesA bit is one binary digit; 8 bits make a byte.
Character encodingASCII and Unicode represent text as binary codes.
Image representationImages stored as pixels with a colour depth.
Sound representationSound sampled at a rate and bit depth to store digitally.
DatabaseAn organised, persistent store of data.
Tables, records & fieldsRows are records; columns are fields.
Primary keyA field that uniquely identifies each record.
SQLLanguage to query and manage a relational database.
Relational databaseLinked tables connected by keys.
QueryA request to select or change data.
Binary TreeEach node has up to two children.
BSTBinary search tree — left subtree smaller, right subtree larger.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What data type is the value 7.0?✗ Integer - 7.0 is a whole number so it must be an integer. ✓ Real (float) - the decimal point makes it a real number in most languages, even though its fractional part happens to be zero.
Which item does a stack remove first?✗ The first item that was added, because items leave in arrival order. ✓ The most recently added item - stacks are LIFO, with both push and pop operating at the top.
A record differs from an array because a record:✗ Must contain elements all of the same type ✓ Can group fields of different data types under one identifier
What does in-order traversal of a binary search tree produce?✗ Nodes in the order they were inserted. ✓ Nodes in ascending sorted order.
What is encapsulation in OOP?✗ Putting code inside other code (nesting). ✓ Bundling data and methods together while restricting direct access to internal state.
Practise Data Structures — free games
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