Programming — AQA GCSE Computer Science

This is the largest topic. It covers the programming constructs and techniques used to write and test programs.

Data types and variables

Common data types: integer, real (float), Boolean, character and string. A variable stores a value that can change; a constant stores a value that does not change. Casting converts between data types.

The three programming constructs

Sequence — statements run in order.
Selection — IF … ELSE and CASE/SWITCH statements make decisions.
Iteration — loops repeat code:
- count-controlled (FOR) — runs a set number of times,
- condition-controlled (WHILE/REPEAT UNTIL) — runs until a condition is met.

Operators

Arithmetic: + − × / , plus integer division (DIV) and modulus (MOD) (remainder).
Comparison: =, ≠, <, >, ≤, ≥.
Boolean: AND, OR, NOT.

Data structures

Arrays (and lists) store multiple values under one name, accessed by an index. They can be one- or two-dimensional.
Records store related fields of different types.
Strings can be manipulated: length, substring, position, concatenation, and converting case.

Subroutines

Procedures and functions are named blocks of code (subroutines). A function returns a value; a procedure does not. They allow parameters to be passed in, support decomposition and reuse, and have local and global variables.

Other techniques

File handling — reading from and writing to text files.
Random number generation.
SQL to query a database (covered separately).
Validation (checking input is sensible) and authentication.

Testing

Programs are tested with normal, boundary and erroneous data to find and fix errors (syntax errors and logic errors).

Exam tips

Learn the three constructs: sequence, selection, iteration.
Know DIV and MOD and the Boolean operators.
A function returns a value; a procedure does not.
Test with normal, boundary and erroneous data; distinguish syntax vs logic errors.