Big Idea 3: Algorithms & Programming | AP CSP Course | APCSExamPrep.com
Big Idea 3 • AAP • 30–35% of AP Exam • 10 weeks full year
Algorithms & Programming
The heaviest Big Idea on the exam and the core of the Create Performance Task. 18 individual lessons covering the full programming toolkit — from variables and expressions through procedures, searching algorithms, and undecidable problems. Every lesson includes a code editor.
🕒 Prerequisites: Complete Big Idea 1 and Big Idea 2 first.
Big Idea 3 is the Create Performance Task
Every concept in these 18 lessons directly maps to the Create Task rubric. Procedures, parameters, lists, algorithms, and iteration are not just exam topics — they are the building blocks of the program you will build and submit. Mastering BI3 is mastering the CPT.
Go to the Create Task module →All 18 lessons
Big Idea 3 Topics
Follow in order. Each lesson builds on the previous. Every lesson includes a game and a live code editor.
Variables & Assignments
Storing, updating, and tracing the value of variables through sequential code
Data Abstraction
Using variables to generalize and manage complexity; what abstraction means in practice
Mathematical Expressions
Arithmetic operators, MOD, integer division, operator precedence, and predicting expression values
Strings
String concatenation, length, substring operations, and predicting string output
Boolean Expressions
AND, OR, NOT operators; truth tables; evaluating compound boolean expressions
Conditionals
IF, IF/ELSE, ELSE IF structures; tracing which branch executes for a given input
Nested Conditionals
IF statements inside IF statements; tracing complex decision trees; avoiding common nesting errors
Iteration
REPEAT N TIMES, REPEAT UNTIL, FOR EACH loops; counting iterations; tracing loop output
Developing Algorithms
Building algorithms using sequencing, selection, and iteration; expressing algorithms in pseudocode and flowcharts
Calling Procedures
How to call a procedure; passing arguments; what RETURN does; tracing procedure calls
Developing Procedures
Writing procedures with parameters; how parameters generalize procedures; procedural abstraction
Libraries
What an API is; how libraries extend what programs can do; using library procedures without knowing their implementation
Random Values
RANDOM(a, b) behavior; predicting the range of possible outputs; using randomness in programs
Simulations
Why simulations are used; what they can and cannot model; how randomness enables simulation
Algorithmic Efficiency
Polynomial vs. exponential time; reasonable vs. unreasonable algorithms; why some problems are hard
Undecidable Problems
Problems that no algorithm can solve for all inputs; the Halting Problem; limits of computation
Highest-frequency concepts
What the Exam Tests in BI3
These appear in almost every released AP CSP exam.
Tracing code
Given a code segment, determine the value of a variable or the output after execution. The single most common question type in BI3.
Conditionals & boolean logic
Evaluate AND/OR/NOT expressions. Identify which branch of an IF/ELSE executes for a given input. Nested conditionals appear frequently.
Loops & iteration
Count how many times a loop executes. Predict the value of a variable after a loop completes. REPEAT UNTIL vs. REPEAT N TIMES behavior.
List operations & indexing
AP pseudocode uses 1-based indexing. Insert, delete, access by index, traverse with FOR EACH. This trips up most students.
Procedures & parameters
Trace a procedure call, identify what RETURN sends back, explain how parameters generalize a procedure. CPT rubric directly tests this.
Efficiency & binary search
How many iterations does binary search need? What makes an algorithm reasonable vs. unreasonable? Polynomial vs. exponential time.
Teaching Big Idea 3?
The AP CSP Teacher Superpack includes editable slides for all 18 BI3 topics, lesson plans with daily pacing, student guided notes, a comprehensive unit test with answer key, and a pseudocode reference sheet.
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