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Big Idea 3: Algorithms and Programming

Ben Davis

Ben Davis

16 min read

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Study Guide Overview

This study guide covers Big Idea 3: Algorithms and Programming for AP Computer Science Principles. It includes: variables, data types, lists, strings, Boolean expressions, conditionals (including nested conditionals), iteration, developing algorithms, binary search, calling and developing procedures, libraries, random values, simulations, algorithmic efficiency, and undecidable problems. The guide emphasizes pseudocode and provides practice questions and exam tips.

AP Computer Science Principles: Big Idea 3 - Algorithms and Programming šŸš€

Welcome to your ultimate study guide for Big Idea 3! This section is HUGE, making up 30-35% of your AP exam, and it's also the core of your Create project. Let's get you ready to ace it!

This unit is a major focus of the AP exam. Master these concepts for a strong score!

The Big Idea: Code Fundamentals

This Big Idea covers the core programming concepts you'll need. Think of it as the building blocks of all the code you'll see on the AP test. It introduces variables, lists, and procedures that are common to most programming languages. Instead of a specific language, the AP CSP test uses Pseudocode, a simplified language that's similar to Python. Remember, all pseudocode examples come from the College Board's Exam Reference Sheet.

3.1 Variables and Assignments

Key Concept

Variables are like containers that hold values. Remember, capitalization matters!

Key Ideas

  • Variables are placeholders for values.
  • Variable names are case-sensitive (e.g., myVar is different from myvar).
  • Data types categorize data (e.g., numbers, text).

Vocabulary

  • Variable: A named storage location in memory.
  • Data Types: Categories of values (e.g., integer, string, boolean).

Resources

šŸ”— 3.1: Variables and Assignments

Practice Question

Multiple Choice:

  1. What is the value of x after the following code is executed?
pseudocode
x ā† 5
x ā† x + 2

(A) 5 (B) 2 (C) 7 (D) Error

  1. Which of the following is NOT a valid variable name?

    (A) my_variable (B) myVariable (C) 1variable (D) myVar1

Free Response:

Write a pseudocode program that declares a variable named age and assigns it your age, then increases it by one, and then prints the new age.

Scoring:

  • 1 point: Correct declaration and assignment of age.
  • 1 point: Correctly incrementing age by one.
  • 1 point: Correctly printing the new value of age.

3.2 Data Abstraction

Key Ideas

  • Lists store multiple elements.
  • Each element has an index (position), starting from 1 in pseudocode.
  • Data abstraction simplifies data for easier program management.

Vocabulary

  • List: An ordered collection of elements.
  • Element: An individual value in a list.
  • Index: The position of an element in a list.
  • String: A sequence of characters.
  • Array: Another term for list (often used interchangeably).

Resources

šŸ”— 3.2: Data Abstraction

Practice Question

Multiple Choice:

  1. What is the value of myList[2] after the following code is executed?
pseudocode
myList ā† [10, 20, 30, 40]

(A) 10 (B) 20 (C) 30 (D) 40

  1. Which of the following best describes data abstraction?

    (A) Making code more complex (B) Simplifying data representation (C) Writing code in multiple languages (D) Using only integers

Free Response:

Create a pseudocode program that initializes a list called scores with three numbers. Then, print the second element of the list.

Scoring:

  • 1 point: Correct initialization of the list scores.
  • 1 point: Correctly accessing and printing the second element of scores.

3.3 Mathematical Expressions

Key Ideas

  • Algorithms are the logic behind problem-solving.
  • Programs execute algorithms step-by-step.
  • The MOD operator gives the remainder of a division.
  • Expressions are evaluated using order of operations (PEMDAS).

Vocabulary

  • Algorithm: A step-by-step procedure for solving a problem.
  • Sequencing: Executing code statements in order.
  • Code Statement: A single instruction in a program.
  • Expression: A combination of values, variables, and operators.

Resources

šŸ”— 3.3: Mathematical Expressions

Practice Question

Multiple Choice:

  1. What is the result of the expression 17 MOD 5?

    (A) 2 (B) 3 (C) 3.4 (D) 12

  2. What is the value of result after the following code is executed?

pseudocode
result ā† 5 + 3 * 2

(A) 16 (B) 11 (C) 10 (D) 13

Free Response:

Write pseudocode to calculate the average of three numbers: 10, 20, and 30. Store the result in a variable called average and print it.

Scoring:

  • 1 point: Correctly summing the three numbers.
  • 1 point: Correctly dividing by 3 to find the average.
  • 1 point: Correctly assigning the result to average and printing it.

3.4 Strings

Key Ideas

  • Strings are ordered lists of characters.
  • Use index values to access characters.
  • String slicing creates substrings.
  • Concatenation joins strings.

Vocabulary

  • String Concatenation: Joining strings together.
  • Substring: A portion of a string.

Resources

šŸ”— 3.4: Strings

Practice Question

Multiple Choice:

  1. What is the result of the expression "hello" + "world"?

    (A) helloworld (B) hello world (C) "hello" + "world" (D) Error

  2. If myString is "computer", what is SUBSTRING(myString, 3, 5)?

    (A) comp (B) mput (C) mpu (D) put

Free Response:

Write pseudocode that declares a string variable called message with the value "Hello, World!". Then, print the substring that contains only "World".

Scoring:

  • 1 point: Correctly declaring and assigning the string to message.
  • 1 point: Correctly extracting and printing the substring "World".

3.5 Boolean Expressions

Quick Fact

Boolean values are either true or false.

Key Ideas

  • Boolean variables store true or false.
  • Relational operators (e.g., <, >, ==) compare values.
  • Logical operators (NOT, AND, OR) combine Boolean values.

Vocabulary

  • Boolean Value: A value that is either true or false.

Resources

šŸ”— 3.5: Boolean Expressions

Practice Question

Multiple Choice:

  1. What is the result of the expression (5 > 3) AND (2 < 1)?

    (A) true (B) false (C) Error (D) None...