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While Loops

Sophie Anderson

Sophie Anderson

7 min read

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Study Guide Overview

This study guide covers iteration using while loops in Java. It explains loop structure, common issues like infinite and skipped loops, and various while loop applications (fixed repetitions, sentinel/flag control). It also discusses the break and continue statements, exception handling with try-catch blocks, and example algorithms. Finally, it provides exam tips focusing on loop logic, exception handling, and common while loop use cases.

🚀 AP Computer Science A: Iteration & Loops - Night Before Review 🚀

Welcome! Let's solidify your understanding of iteration and loops. This guide is designed to be your quick, high-impact review for the exam. Let's get started!

🔄 Introduction to Iteration

Key Concept

Iteration is the process of repeating a block of code until a condition is met. We achieve this using loops.

  • Two primary loop types:
    • while loop: Repeats as long as a condition is true.
    • for loop: (Covered later, but mentioned for context).
    • Enhanced for loop: (Unit 6, not covered here).

⏳ while Loops: Anatomy and Function

Key Concept

A while loop executes a block of code repeatedly as long as a specified condition remains true.

java
// Code before the loop
while (condition) {  // Condition is a boolean expression
  // Loop body: Code to be repeated
}
// Code after the loop (executed when condition is false)
  • Condition: A boolean expression that determines if the loop continues.
  • Loop Body: The code block that is executed repeatedly.
  • Exiting the Loop: The loop terminates when the condition becomes false or a return statement is encountered within the loop body.

⚠️ Potential Loop Issues

Common Mistake

Be careful with loop conditions! Incorrect conditions can lead to infinite loops or skipped loops.

♾️ Infinite Loops

  • Occurs when the loop condition always evaluates to true.
  • Example: Forgetting to update a counter variable.
  • Avoid at all costs! Can crash your program.
  • Emergency Exit: Use Ctrl + C to stop an infinite loop.

🚫 Skipped Loops

  • Occurs when the loop condition is always false.
  • The loop body is never executed.
  • Indicates a logical error in your code.

⚙️ Common while Loop Structures

🔢 Fixed Number of Repetitions

  • Uses a counter variable to control the number of iterations.
java
int i = 0; // Initialize counter
while (i < numberOfRepetitions) {
  // Do something
  i++; // Increment counter
}
  • Increment (i++) is crucial! Without it, you'll get an infinite loop.

🛑 Variable Repetitions with a Sentinel

  • Loop continues until a specific input (the sentinel) is entered.
java
im...
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