AP Computer Science Principles Reference Sheet 2026
Pseudocode syntax · Big Ideas vocabulary · Binary & data · Internet protocols · Cybersecurity
AP CSP Pseudocode Syntax
| Statement | Example |
|---|---|
| Assignment | x ← 5 |
| Display output | DISPLAY(x) |
| Input | x ← INPUT() |
| Arithmetic | + − * / MOD |
| String concat | "Hello" + name |
| Comparison | = ≠ < > ≤ ≥ |
| Boolean ops | AND OR NOT |
| IF / ELSE IF | IF (cond) { ... } ELSE { ... } |
| FOR loop | FOR EACH item IN list { ... } |
| REPEAT N times | REPEAT n TIMES { ... } |
| REPEAT UNTIL | REPEAT UNTIL (cond) { ... } |
| Procedure def | PROCEDURE name(params) { ... } |
| Call procedure | name(args) |
| Return value | RETURN (value) |
| List creation | myList ← [1, 2, 3] |
| List access | myList[i] (1-indexed) |
| List insert | INSERT(myList, i, val) |
| List append | APPEND(myList, val) |
| List remove | REMOVE(myList, i) |
| List length | LENGTH(myList) |
5 Big Ideas & Key Concepts
Each Big Idea has a color-coded badge below.
BI 1 Creative Development
Iterative design process · Collaboration · Abstraction to manage complexity · Procedural abstraction · Program documentation
BI 2 Data
Binary representation · Overflow · Lossless vs. lossy compression · Metadata · Data aggregation · Privacy implications · Machine learning from data · Correlation ≠ causation
BI 3 Algorithms & Programming
Sequencing, selection, iteration · Variables, parameters, return values · Boolean logic · Recursion · Linear vs. binary search · Algorithm efficiency (runtime) · Heuristics · Undecidable problems
BI 4 Computer Systems & Networks
Packet switching · DNS · HTTP/HTTPS · IP addresses · Fault tolerance · Open protocols · TCP/IP layers · Bandwidth vs. latency · Sequential vs. parallel computing
BI 5 Impact of Computing
Digital divide · Privacy (PII, aggregation, tracking) · Intellectual property · Creative Commons · Net neutrality · Cybersecurity threats · Bias in algorithms · Beneficial & harmful effects
Binary & Data Representation
| Concept | Rule / Example |
|---|---|
| Binary (base-2) | Digits: 0, 1 only. 1010₂ = 10₁₀ |
| Bit positions | Right to left: 2⁰, 2¹, 2², 2³... (1, 2, 4, 8...) |
| n bits → values | 2ⁿ distinct values (0 to 2ⁿ − 1) |
| 8 bits = 1 byte | 256 possible values (0–255) |
| Hexadecimal | Base-16: 0–9 then A=10, B=11...F=15 |
| Overflow | Result exceeds max bits → wraps or error |
| Roundoff error | Floating-point can't represent all decimals exactly |
| Lossless compress | Original fully recoverable (ZIP, PNG, run-length) |
| Lossy compress | Data permanently discarded (JPEG, MP3) |
| RGB color | 3 × 8 bits = 24-bit = 16.7 million colors |
| Analog → digital | Sampling: higher sample rate = more accurate |
Internet & Network Concepts
| Term | Definition |
|---|---|
| IP address | Unique identifier for each device on a network |
| DNS | Translates domain names → IP addresses (Internet's phonebook) |
| Packet switching | Data split into packets; each may take different routes |
| HTTP | Protocol for web data transfer; plaintext |
| HTTPS | HTTP + TLS encryption; data is encrypted in transit |
| Bandwidth | Maximum data transfer rate (bits per second) |
| Latency | Time delay for data to travel from source to destination |
| Fault tolerance | System continues working even if components fail (redundancy) |
| Open protocols | Publicly documented standards; anyone can build compatible software |
| Sequential | Steps executed one at a time |
| Parallel computing | Multiple tasks execute simultaneously on multiple processors |
| Distributed computing | Multiple networked computers work together on one problem |
Cybersecurity & Privacy
| Term | Definition |
|---|---|
| Authentication | Verifying identity (password, 2FA, biometrics) |
| Authorization | Granting permission to access a resource |
| Encryption | Transforming data so only authorized parties can read it |
| Phishing | Deceptive attempts to steal credentials (fake emails/sites) |
| Malware | Software designed to damage or gain unauthorized access |
| Ransomware | Malware that encrypts data and demands payment |
| DDoS | Distributed Denial of Service — overwhelming a server with traffic |
| PII | Personally Identifiable Information — data that identifies a person |
| Data aggregation | Combining multiple data points to reveal sensitive information not apparent from individual pieces |
| Metadata | Data about data — e.g., who sent a message, when, from where |
| Cookie | Small data file stored by a browser to track sessions/preferences |
| Digital footprint | All data about a person created by their online activity |
Impact of Computing — Key Terms
| Term | Definition |
|---|---|
| Digital divide | Unequal access to computers and internet across populations |
| Net neutrality | ISPs must treat all internet traffic equally (no blocking/throttling) |
| Creative Commons | Licenses that specify conditions for use/sharing while retaining copyright |
| Open source | Software with publicly available source code; anyone can modify/distribute |
| Algorithmic bias | Systematic unfairness in AI/algorithm outputs due to biased training data |
| Filter bubble | Algorithms show only content matching prior preferences, reducing exposure to other views |
| Crowdsourcing | Obtaining input/work from a large online group |
| Citizen science | Public volunteers contribute data to scientific research using technology |