Lesson 3.2: Combining Loops and Conditionals¶

Learning Objectives¶

Students will be able to…

Combine loops with conditionals to create models with repeated but conditional behavior.

Duration	Description
5 minutes	Welcome, attendance, bell work, announcements
10 minutes	Review, lecture and introduce activity
30 minutes	Gravity activity
10 minutes	Review and wrap-up

Ask students what loops do, when they are useful, and what loops exist in Snap!.
- Loops cause code to execute multiple times.
- Loops can help reduce redundancy and increase readability.
- Snap! contains three loops: repeat, forever, and repeat until.
Ask students what conditionals are for and when they are useful.
- conditionals are used to execute a block of code only under certain circumstances.
- Encourage discussion about previous activities.
- Fill in understanding gaps when necessary.

Present repeat until and forever if blocks.
Ask students to suggest when these constructs might be useful.
- repeat until is useful when a loop needs to run not for a set number of iterations, but until some situation occurs.
- forever if is useful when a script should execute any time a condition is true, for the duration of the program.
- Point out that the condition in repeat until is a termination condition, while in forever-if it is a continuation condition.

Modeling: building a system to simulate the behavior of a real-life phenomenon by simplifying or ignoring certain details.
Ask students to suggest systems or concepts that might need to be modeled.
Discuss important considerations when designing and implementing a model.
- Lead students to realize that most sacrifice some amount of accuracy or realism for simplicity.

Students should complete “What Goes Up…” lab individually.
Mention that the script written in this lab will be helpful for the end of unit project.

Take care to ensure that all students have a functional script by the end of the lab to avoid putting some students at a disadvantage starting the project.
If many students struggle, consider releasing your own solution after the lab has been completed in class.
Ask the more advanced students to assist struggling students. It is vital that all students complete this lab in advance of starting the project.
Advanced students can consider increasing the realism of their gravity model by adding acceleration and/or beginning to implement jumping.