Programming
Programming is the process of writing instructions that a computer can follow to solve a problem. AQA GCSE Computer Science covers programming using a high-level language (typically Python) alongside AQA pseudocode. This section spans all the core concepts you need to write and understand programs.
What this section covers
Data types (CS2.1)
Every value in a program has a data type — integer, real (float), Boolean, character or string. Choosing the right type ensures data is stored correctly and operations work as expected.
Programming concepts (CS2.2)
The building blocks of every program:
- Variables and constants — named storage locations for values
- Sequence — instructions execute one after another
- Selection (IF/ELIF/ELSE) — different paths based on a condition
- Iteration (WHILE / FOR) — repeating a block of code
Arithmetic and relational operations (CS2.3, CS2.4)
Programs compute using arithmetic (+, -, *, /, DIV, MOD, ^) and compare values using relational operators (=, ≠, <, >). Boolean operators (AND, OR, NOT) combine conditions.
Data structures (CS2.5)
Arrays (1D and 2D) store multiple values of the same type. Records group related fields. Choosing the right structure simplifies code.
Input, output and file handling (CS2.6)
Programs interact with users through input and output, and persist data by reading from and writing to text files.
String handling (CS2.7)
Common string operations: finding length, extracting substrings, concatenation, changing case, converting to/from ASCII values.
Random numbers (CS2.8)
RANDOM() generates pseudo-random numbers — important for games, simulations and testing.
Subroutines (CS2.9)
Procedures and functions group reusable code. Functions return values; procedures do not. Parameters pass data in; local variables are hidden from the rest of the program.
Structured programming (CS2.10)
Top-down design, decomposition, modularity and abstraction make large programs manageable.
Robust and secure programming (CS2.11)
Validation (range, type, length, presence checks), authentication and defensive programming protect against bad input and misuse.
Languages and translators (CS2.12)
High-level languages are readable and portable; low-level languages give direct hardware control. Assemblers, compilers and interpreters translate code into machine-executable form.
The programming mindset
Good programmers:
- Understand the problem before writing any code
- Design an algorithm (pseudocode or flowchart)
- Implement in a chosen language
- Test with normal, boundary and erroneous data
- Debug and iterate until correct
Every topic in this section builds towards writing programs that are correct, readable and robust.
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