Lesson 4: Input Unplugged



In preparation for delving deeper into programming with App Lab, students will explore how a handful of different programs written in both Game Lab and App Lab handle taking input from the user. After comparing and contrasting the approaches they saw in the example apps, students group up to act out the two different models for input (conditionals in an infinite loop and asynchronous events) to gain a better understanding of how they work.


This lesson is intended to help students transition from the draw loop and conditional model of input used in Game Lab to the event-driven model used in App Lab. While students have experienced and learned a bit about event-driven programming in Unit 4, a deeper understanding of how the events work will help when it comes to responding to events on the Circuit Playground later in this unit.

Assessment Opportunities

  1. Compare and contrast multiple ways to take input

    Wrap Up: Students should distinguish between the draw loop model of Game Lab and the event model of App Lab.

  2. Model different methods of taking user input

    As students participate in the activity, circulate the room and ensure that they are following the instructions.


Lesson Modifications

Warm Up (10 min)

Activity (40 min)

Wrap Up (2 min)

View on Code Studio


Students will be able to:

  • Compare and contrast multiple ways to take input
  • Model different methods of taking user input


  • Prepare to display example programs for the whole class.
  • A half deck of cards for each group of three students or deck-of-cards.js.org.
  • Print one copy of the activity guide for each group of four students.


Heads Up! Please make a copy of any documents you plan to share with students.

For the Students

Teaching Guide

Lesson Modifications

Attention, teachers! If you are teaching virtually or in a socially-distanced classroom, we have recommendations for alternate lessons that can be used for this unit on physical computing. Click Here to read our recommendations for Unit 6.

Warm Up (10 min)

Maker App Updates

For Windows & Mac users: we've recently updated the way that students can log in with Google using the Maker App. Please see this forum post for more information about these updates and how to continue using Google to log in to the Maker App.

Comparing Input Methods

Discussion Goal

Goal: This is intended to be a very broad question, and as such could go in a number of different directions. If your students are struggling, encourage them to think about specific programs that they wrote in units 3 and 4.

Discuss: Yesterday we wrote some apps that took input from a user, but how did the program know when to take input?

Display: Open up the Code Studio stage for this level. For each of the example apps, ask the class to identify:

  1. Where is the input coming from? (e.g. keyboard, mouse, etc)
  2. What input value is the program looking for?
  3. How will the program respond to input?

Prompt: Ask the class the following questions, keeping track of answers on the board. The goal at this point isn't to answer questions that come up, but to record them so we can see how the class feels again after the lesson.

  • How did the different apps we looked at approach taking input similarly or differently?
  • Which way made the most sense to you?
  • Which way made the least sense?
  • What questions to you have about how these programs take input?

Activity (40 min)

Input Unplugged


In the previous activity we explored several different kinds of input, but how do our programs actually process that input? As a class, and in small groups, we're going to model how input is taken both in Game Lab and App Lab.

Group: Place students in groups of 4

Distribute: Hand out a copy of the activity guide and half of a deck of cards to each group (the deck doesn't need to be perfectly split, but should include both red and black cards in each half). The activity guide includes four different role pages, printed front and back.

Model: Choose one group to model the activity for the class.

Input and Events

The goal of this activity is to help students better understand how events work, and how using events differs from the input model that they used in Game Lab. In groups of four, students will model the two different approaches to taking input. By the end of the activity students should understand that the onEvent block sets up a input to watch for events in the background, allowing input handling without explicitly asking each input for a value constantly. The roles for this activity are:

Program: The Program reads the code aloud and performs any actions dictated by the inputs. Inputs 1-3: The Inputs draw cards from the deck, which represent their changing input values.

Version A: Asking for Input

Teaching Tip

The programs for both versions of this activity are purposely very simple to allow students to focus on the processes involved in each input method. If your students pick up on the ideas quickly, consider providing some more detailed example programs to push on their understanding. In particular, placing the inputs or events in a different order and nesting conditionals can be useful in revealing misconceptions.

This first version models the Game Lab approach to taking input. In this scenario the Program explicitly asks each input for a value every time the draw loop is run.

Rules for Version A:

  • The Program reads each line of code aloud.
  • At the beginning of each draw loop, each Input draws a new card from the deck. This represents the current state of that input.
  • Whenever the Program reaches an input checking command (inputOne(), inputTwo(), or inputThree()), the Program asks to see that inputs card.
  • If the value of the card shown matches the associated conditional, the Program performs the action(s) inside the conditional.

After groups have run the program a few times and seem to understand how it works, have them switch up roles so that each student gets a chance to be the Program.

Version B: Input Events

This time around, instead of constantly asking for input in a loop, the Program will assign each Input an Event to watch for. In the context of this activity, an Event is either a red or black card, but in a program that Event could be a click on a button, movement of the mouse, press of a key, or more. This is a simplified model for the way input is handled in App Lab.

Rules for Version B:

  • Each Input draws a card from the deck at a rate of roughly one per second.
  • The Program reads each line of code aloud.
  • When the Program reaches an onEvent command, they tell the specified Input which Event to watch for, and what the Response should be.
  • When assigned an Event, the Input writes down the details in their Events to Watch table.
  • Every time an Input draws a card, they check to see if it matches one of the Events in their table. If it does, they tell the Program to perform the Response.

There are a few important simplifications that are made in this model to minimize the number of roles and rules:

  • This model implies that Inputs are actually watching for Events on their own. In reality, an Event Handler running in the background watching for the specified event.
  • In this model the Input tells the Program what actions to take. In reality, when an Event Handler is triggered, the Program goes to that portion of their code and runs everything in the function.

Activity Debrief

Discuss: Looking back at the comments gathered from the warm up activity, what things are more clear after having run the activity? Do you have any new questions?

Wrap Up (2 min)

Assessment Opportunity

Students may have different ways of explaining the differences, but Game Lab's draw loop model works sequentially, with each line of code run after the other, and the draw loop code running over and over in sequence. Inputs are only checked when that line of code is run. App Lab's event model is continuously checking for inputs once an event handler is created.


Journal: What's the difference between the way that Game Lab and App Lab handle inputs?

  • Input Examples
  • 2
  • 3
  • (click tabs to see student view)
View on Code Studio

Student Instructions

Input in Game Lab

You don't need to make any changes to the code here

Take a minute to read through the code and run the program. Discuss with a partner:

  1. What is the source of input?
  2. Where and how does the program check for input?
  3. What does the program do when it gets the correct input?
  4. What is the program doing when there is no input?
View on Code Studio

Student Instructions

Input in App Lab

You don't need to make any changes to the code here

Take a minute to read through the code and run the program. Discuss with a partner:

  1. What is the source of input?
  2. Where and how does the program check for input?
  3. What does the program do when it gets the right input?
  4. What is the program doing when there is no input?

Standards Alignment

View full course alignment

CSTA K-12 Computer Science Standards (2017)

AP - Algorithms & Programming
  • 2-AP-10 - Use flowcharts and/or pseudocode to address complex problems as algorithms.