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IB Computer Science: B2 · Programming

Data types, control structures, files, searching and sorting. 5 subtopics, 21 key terms.

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In this topic: B2.1 · B2.2 · B2.3 · B2.4 · B2.5

B2.1Programming fundamentals

Variable: A named storage location whose value can change.
Data type: The kind of data a variable holds: integer, float, string, Boolean.
Selection: Choosing a path with if / else if / else.
Iteration: Repeating code: count-controlled (for) or condition-controlled (while).
Exception: An error at run time that can be handled (try / except).

Operators: arithmetic (+ − * / // % **), comparison (== != < > <= >=), logical (and, or, not). // is integer division and % is the remainder.

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: Know the difference between = (assignment) and == (comparison): a classic error to spot in code questions.

Array: A fixed-size collection of elements of the same type, accessed by index.
List: A dynamic collection that can grow and shrink (Python list, Java ArrayList).
2D array: An array of arrays, like a table with rows and columns.
Index: The position of an element; usually starting at 0.

Static structures have a fixed size (fast, memory-efficient); dynamic ones resize (flexible, some overhead).

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: When looping with an index, remember the last valid index is len − 1.

Function / method: A named block of code that performs a task and can return a value.
Parameter / argument: A variable in a function definition / the value passed in when it is called.
Scope: Where a variable can be accessed: local (inside a function) or global.
Recursion: A function that calls itself, with a base case to stop.

Benefits of modules: reuse, easier testing and debugging, teamwork, readability, abstraction.

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: For recursion questions, write each call on a new line, then unwind from the base case upwards.

Linear search: Checks each element in turn; works on unsorted data; O(n).
Binary search: Repeatedly halves a sorted list; O(log n).
Bubble sort: Repeatedly swaps adjacent elements that are out of order; O(n²).
Selection sort: Repeatedly selects the smallest remaining element and moves it into place; O(n²).
Big O notation: Describes how running time grows with input size n in the worst case.

Binary search on 1 million sorted items needs at most about 20 comparisons (\(2^{20}\approx10^{6}\)); linear search may need 1 million.

The full notes, worked example, interactive diagram and check questions for this subtopic are in the app.

Exam tip: Binary search only works on sorted data: say so whenever you choose it.

File mode: How a file is opened: read ('r'), write ('w', overwrites), append ('a').
Text file: Stores characters, often one record per line (e.g. CSV).
Persistence: Keeping data after the program ends.

Steps: open → read or write → close (using with closes automatically).

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: Always strip the newline character from lines read from a file before converting them.