Appropriate libraries or APIs (College Board AP® Computer Science Principles): Study Guide

Using libraries and APIs

What is a library?

• A library is a collection of pre-written procedures that can be imported and used in a program

• Libraries provide tested, reusable code so programmers do not need to write common functionality from scratch

• Code can come from existing libraries, other programmers, or online sources

What is an API?

• An API (Application Programming Interface) is a set of rules and specifications that defines how procedures in a library can be used

• APIs tell the programmer what procedures are available, what parameters they accept, and what values they return

• Using a library simplifies development because the programmer only needs to understand the API, not the internal implementation

API documentation and specifications

• API documentation describes how to use each procedure in a library: its name, parameters, return values, and behavior

• Programmers read the documentation to understand what a procedure does without needing to read its source code

• Well-written documentation includes examples showing how to call the procedure correctly

Random value generation

How does random value generation work?

• The RANDOM function generates a random integer between two specified values (inclusive)

• In AP CSP pseudocode: RANDOM(a, b) returns a value where a ≤ result ≤ b

• Each time RANDOM is called, it may produce a different result, even with the same arguments

roll ← RANDOM(1, 6)
DISPLAY(roll)
 

• This simulates a dice roll by generating a random integer from 1 to 6

Using random values in programs

• Common uses include: simulating events, generating test data, and creating games

• Repeated runs of the same program may produce different outputs when RANDOM is used

REPEAT 3 TIMES
{
   DISPLAY(RANDOM(1, 10))
}
 

• Each execution displays three random numbers between 1 and 10, potentially different every time