GCSE Computer Science: Algorithms and Programming Fundamentals Guide

Representing algorithms

Algorithms can be represented as pseudocode (structured, code-like instructions in plain language) or flowcharts (diagrams using standard symbols for steps, decisions and processes).

Programming constructs

All programs are built from sequence (instructions in order), selection (if/else decisions) and iteration (for/while loops), along with variables to store data that can change while a program runs.

Searching algorithms

Linear search checks every item one by one until it finds a match, working on any list but slower for large ones. Binary search repeatedly halves a sorted list to find a match much faster, but only works if the list is already sorted.

Sorting algorithms

Bubble sort repeatedly compares and swaps adjacent items until the list is in order. Merge sort splits the list into smaller lists, sorts them, then merges them back together, and is generally faster for large datasets.

Common mistakes

• Using binary search on an unsorted list — it requires the list to be sorted first.
• Confusing selection (a decision) with iteration (a repeat).
• Describing what an algorithm does without being able to trace through it step by step.