Lesson 3: For Loops

Data helps us find trends and even make predictions about our society. This visual shows us the popularity and revenues of music formats over the years.

Discuss: Click through the animated slide to display the prompts.

• What surprises you about this data?
• What information would be stored in a data structure? How could a program determine these results?
• What questions could someone answer with this data? What problems might this help address?

Discussion Goal: Students may be surprised that streaming and downloading music has led to decreased revenue in comparison to CDs. Students suggest that a data structure would store revenue for each year or revenue for each format. Students also suggest that a program would add up the values for each year or each format so it could be displayed in this visual.

Ask students to identify the specific data points in the visual, such as the total revenue for each year and each format. You can also have students consider the appropriate data types for each type of information.

To find this type of information from a set of data, software engineers use loops to go through a data structure and perform searches and calculations. In the previous lesson, we used a while loop to access and print all the values in a 1D array.

Do This: Review the lesson objectives.

Display: Show the video – For Loops.

Do This: Click through the animated slide to identify the components of a for loop.

Have students compare a for loop to a while loop. Ask students where the parts of a for loop are present in a while loop.

Do This: Click through the animated slide to explain the functionality of the increment and decrement operators.

Do This: Click through the animated slide to demonstrate writing a trace table to trace a for loop.

Model tracing the first two iterations of the loop, then ask students to assist in completing the rest of the trace table.

Do This: Click through the animated slide to define traverse and demonstrate traversing a 1D array with a for loop.

Point out to students that the condition is less than the length of the array rather than less than or equal to its length. Have students identify the length and the last index of the array in the code segment. Ask students to predict what might happen if the condition was less than or equal to the length and trace the code to demonstrate the result.

Distribute: Give each student a copy of the Tracing Loops handout.

Do This: Have students complete the Tracing Loops handout.

Discuss: Use the Hold That Thought strategy to discuss the prompt.

• How can we tell how many times a for loop will execute?

Discussion Goal: Students note that the number of times is determined by counting from the value the loop control variable is initialized to and the value that stops the loop.

Have students refer to the Tracing Loops handout if they struggle to identify the number of times a for loop will execute. Ask students to compare their trace table to the starting value of the loop control variable and the condition to identify the relationship.

for loops are much easier to use with 1D arrays, but both a while loop and a for loop can be used interchangeably.

Do This: Direct students to Level 1 on Code Studio to complete Levels 1 through 3. Students complete a Check for Understanding on Level 1, then continue to Level 2 to convert a while loop to a for loop. On Level 3, students complete a choice level to use a for loop with a 1D array in the console or The Neighborhood.

Do This: Click through the animated slide to have students participate in the Code Review Call and Response.

Do This: Direct students to complete a code review on Level 4.

We have learned a lot about using loops to repeat a block of code and traverse 1D arrays. Let's recap some of the key concepts we have learned.

Discuss: Click through the animated slide to display the prompts.

• What are some differences between while loops and for loops? What are some similarities?
• What are some scenarios you have encountered before where a for loop would have been better to use?
• What were you confident about in this lesson? What would you like to practice?

Discussion Goal: Students identify similarities and differences between while loops and for loops, such as that both loops have the same components but are structured differently in each type of loop. Students suggest using a for loop to traverse a 1D array and for situations when the number of times to repeat a block of code is known. Students share concepts from the lesson and the unit they are confident about and concepts they might be confused about.

Do This: Review the concepts covered in this lesson.

Display: Key Vocabulary

Check For Understanding Question(s) and solutions can be found in each lesson on Code Studio. These questions can be used for an exit ticket.

To assign questions from the AP Classroom Question Bank that align with this lesson, create a custom quiz in AP Classroom by searching the Question Bank for the Essential Knowledge statements listed at the top of this lesson plan. You can find instructions and video demonstrations to do this on AP Central.

The following Topic Questions in AP Classroom can be assigned as a formative assessment for this lesson:

• Topic Questions 4.2
• Topic Questions 6.2

Note: Some Learning Objectives and Essential Knowledge statements in the suggested Topic Questions are covered in later units.