AP Computer Science Principles cheat sheet

A program is an ordered set of instructions; a code segment is a portion of that program.

Iterative development: build a small version, test it, revise, repeat; each cycle is an iteration.

Incremental development: add one small piece of functionality at a time and test before adding more.

A procedure abstracts a set of steps behind a name so it can be called repeatedly without rewriting the steps.

Parameters are the input names in a procedure definition; arguments are the actual values supplied in a call.

Documentation records purpose, inputs, outputs, and constraints of a program or procedure for other programmers.

Software licenses (open source vs. proprietary) determine whether code may be reused, modified, or redistributed.

Pair programming divides work into a driver who types and a navigator who reviews, catching errors earlier.

Binary uses base 2: each bit position is a power of 2, so n bits represent 2^n distinct values.

Bit, byte, kilobyte hierarchy: 8 bits = 1 byte; 1 kilobyte = 1024 bytes (or 1000 in decimal prefixes).

Lossless compression preserves all data and is reversible (e.g., PNG); lossy compression discards detail and is not reversible (e.g., JPEG).

Sampling rate and bit depth determine how faithfully analog data such as sound is captured in digital form.

Metadata is data about data (e.g., a photo's timestamp and location) and can reveal information not intended to be shared.

Cleaning data removes errors, duplicates, and outliers; filtering selects a subset of records for analysis.

A data table organizes records as rows and attributes as columns; a record is one complete row of related fields.

Correlation between two variables does not establish that one causes the other.

Sequencing runs statements in order; selection uses conditions (if/else); iteration repeats (for/while loops).

A Boolean expression evaluates to true or false; AND requires both operands true, OR requires at least one, NOT negates.

Linear search checks elements one by one (O(n)); binary search requires sorted data and halves the range each step (O(log n)).

Reasonable time: linear and binary search are reasonable; brute-force problems with exponential growth are not.

A procedure call passes arguments; values passed by value are copied, so changing the parameter does not alter the original variable.

A list (array) stores ordered elements accessed by index; traversal uses a loop to visit each element in turn.

An algorithm is a finite sequence of unambiguous steps that solves a problem; equivalent algorithms may differ in efficiency.

Debugging strategies: add output statements, test boundary cases, and trace variable values step by step.

The Internet is a network of networks using TCP/IP; the World Wide Web is an application layer service running on it.

IP addresses identify devices; DNS translates human-readable domain names into IP addresses.

TCP guarantees ordered, reliable delivery by acknowledging packets and retransmitting lost ones; UDP is faster but unreliable.

Packet switching splits messages into packets routed independently, tolerating partial network failure.

Bandwidth is the maximum data rate of a link; latency is the delay for data to travel; both affect performance.

The fault-tolerant design of the Internet means no single device failure disables the whole network.

Sequential computing does one operation at a time; parallel computing distributes work across multiple processors.

Distributed computing splits a task across networked machines, improving speed but adding coordination overhead.

Computing innovations create benefits and harms; the same technology can have different effects on different groups.

Personally identifiable information (PII) is data that can identify an individual directly or by combination.

Encryption protects data in transit; symmetric uses one shared key, public-key uses a public/private key pair.

Phishing and social engineering exploit human trust rather than technical flaws; multifactor authentication reduces risk.

Open access and open source lower barriers to use but raise questions about support and sustainability.

Bias in data or algorithms can produce unfair outcomes, so datasets and models require scrutiny.

Digital divide: unequal access to computing devices and connectivity can widen existing social and economic gaps.

Legal and ethical concerns include intellectual property, privacy, and the societal consequences of automation.