Day 9: Iteration (Loops) - Part 2

Learning Objectives

• AAP-2.H: For iteration: Write iteration statements.
• AAP-2.I: For iteration: Determine the result or side effect of iteration statements.
• AAP-2.J: Express an algorithm that uses iteration without using a programming language.
• AAP-2.K: For iteration: Determine the result or side effect of iteration statements.

Essential Questions

• When should we use condition-controlled loops instead of count-controlled loops?
• How do we design loops that continue until a specific condition is met?

Materials Needed

• Presentation slides on condition-controlled loops
• Programming environment
• Loop conversion worksheet
• Problem-solving scenarios for loops
• Exit ticket templates

Vocabulary

• Condition-controlled loop
• While loop
• REPEAT UNTIL
• Loop condition
• Termination condition
• Infinite loop
• Pre-test loop
• Iteration

Procedure (50 minutes)

Opening (8 minutes)

1. Review and Connection (3 minutes)

   • Review count-controlled loops from previous lesson
   • Connect to today's focus on condition-controlled loops

2. Warm-up Activity (5 minutes)

   • Present a scenario where the number of repetitions is not known in advance (e.g., keep asking for input until a valid value is entered)
   • Ask students how they might approach this with what they know so far
   • Introduce the need for loops that run until a condition is met

Main Activities (32 minutes)

3. Lecture: Condition-controlled Loops (While Loops) (12 minutes)

   • Introduce condition-controlled loops (while loops):
     • Structure and syntax: REPEAT UNTIL(condition)
     • How the loop condition works
     • Execution flow in a condition-controlled loop
     • When to use condition-controlled loops
   • Explain that the loop continues until the condition becomes true
   • Discuss the concept of pre-test loops (condition checked before execution)
   • Explain common patterns and use cases for while loops:
     • Processing input until a sentinel value
     • Finding values that meet certain criteria
     • Implementing algorithms with unknown iterations
   • Discuss infinite loops and how to avoid them
   • Explain the importance of ensuring the loop condition will eventually be true

4. Demo: Implementing While Loops in Code (8 minutes)

   • Walk through examples of programs with while loops:
     • Validating user input
     • Finding the first number that meets a condition
     • Implementing a guessing game
     • Processing data until a threshold is reached
   • Show how to trace the execution of while loops step by step
   • Demonstrate how the loop condition is evaluated each time
   • Highlight common patterns and techniques with while loops
   • Show examples of infinite loops and how to fix them

5. Hands-on: Converting Between Loop Types (12 minutes)

   • Students work in the programming environment
   • Guide students through converting between for loops and while loops
   • Have students implement the same task using both loop types
   • Discuss when each type is more appropriate
   • Have students identify scenarios where one loop type is clearly better than the other
   • Encourage students to trace their loops manually to understand execution flow

Closing (10 minutes)

6. Activity: Solving Problems with Appropriate Loop Structures (5 minutes)

   • Provide students with various problem scenarios
   • Students determine which loop structure is most appropriate for each scenario
   • Implement one of the scenarios using the chosen loop structure
   • Share and discuss different approaches
   • Highlight the decision-making process for choosing loop types

7. Exit Ticket and Preview (5 minutes)

   • Students create a program that uses the appropriate loop structure for a given problem
   • Preview that next class will focus on nested control structures

Assessment

• Formative: Quality of loop implementation and conversion during hands-on activities
• Exit Ticket: Correctness of loop structure choice and implementation

Differentiation

For Advanced Students

• Provide more complex looping challenges
• Introduce do-while loop concept (post-test loop)
• Challenge them to implement algorithms requiring sophisticated loop control

For Struggling Students

• Offer more structured templates for while loops
• Provide step-by-step tracing guides
• Focus on clear termination conditions to avoid infinite loops

Homework/Extension

• Complete a worksheet with while loop exercises
• Create a program that uses both for loops and while loops appropriately
• Research real-world algorithms that use condition-controlled loops

Teacher Notes

• Emphasize the difference between count-controlled and condition-controlled loops
• Watch for infinite loops in student code
• Make connections to real-world scenarios where the number of repetitions is unknown
• Consider using analogies like "keep stirring until the mixture thickens"
• Remind students that choosing the right loop structure makes code more readable and efficient