Conditionals Chapter Notes | AP Computer Science Principles - Grade 9 PDF Download

Introduction

Conditionals are an essential part of programming in AP Computer Science Principles, allowing programs to make decisions based on specific conditions. This chapter focuses on selection statements, particularly if statements, which control the flow of a program by executing different code blocks depending on whether a condition is true or false. It also covers else statements, which handle situations when the condition is not met. Understanding conditionals helps programmers create flexible code that responds to different scenarios.

Selection Statements

• Selection statements decide which parts of a program run based on specific conditions.
• They control the flow of a program by checking if certain requirements are met.
• Conditionals, like if statements, are a common type of selection statement.
• They use Boolean expressions, which evaluate to true or false, to make decisions.

If Statement 

• An if statement runs a block of code only if its Boolean condition is true.
• If the condition is false, the code inside the if statement is skipped.
• In pseudocode:
  • IF (condition) { block of statements }
  • The block of statements runs if the condition is true; otherwise, no action is taken.
• Example in Python:
  • If strawberries_in_fridge = 7, the condition strawberries_in_fridge >= 7 is true.
  • The code prints: "You can make strawberry shortcake!"
  • If strawberries_in_fridge is less than 7, the program skips the print statement.

Else Statement

• An else statement provides an alternative block of code to run when the if condition is false.
• It only executes if the if statement’s condition evaluates to false.
• In pseudocode:
  • IF (condition) { first block of statements } ELSE { second block of statements }
  • If the condition is true, the first block runs; if false, the second block runs.
• Example in Python:
  • If strawberries_in_fridge = 7, the condition strawberries_in_fridge >= 10 is false.
  • The else block runs, printing: "Sorry, no shortcake for you!"
  • If strawberries_in_fridge >= 10, the if block would run instead, printing: "You can make strawberry shortcake!"

Key Terms

• Conditional Statements: Programming constructs that allow different code blocks to execute based on specific conditions. They enable decision-making in programs by evaluating whether a condition is true or false.
• Else Statements: A component of conditional statements that specifies a block of code to execute when the associated if condition evaluates to false.