3.03: Introducing Functions

Warm up

Ask learners to think about playground games they have played. Can they remember a game they regularly won because they discovered a good tactic, or one where another player always seemed to win using the same strategy? Did it ever feel like they had a "secret trick"?

Some examples include

• Simon Says
• Duck, Duck, Goose
• Capture the Flag
• Dodgeball
• Three-legged Race
• Hide and Seek

Using “Duck, Duck, Goose” as an example, discuss the different strategies for each role in the game.

For someone sitting in the circle:

• Watch the person moving around the circle.
• Prepare to stand by placing hands on the ground.
• Keep feet planted and knees bent, ready to move quickly.

For the person walking around the circle:

• Watch for distracted players.
• Avoid choosing someone who is already watching closely.
• Be ready to move as soon as you tap someone.

Explain that these strategies are similar to **functions** in programming. Each role has a specific set of actions that can be repeated whenever that role is performed. Rather than writing those actions over and over again, programmers group them into functions that can be reused whenever needed.

Working in small groups, ask learners to choose one playground game and research the rules if necessary. They should identify:

• how the game is played
• whether there are teams or individual player
• how a winner is decided
• one tactic that gives a player the best chance of winning

Get learning

Once groups have chosen a tactic, ask them to write it as pseudocode and give it a meaningful function name. They should then explain where that function would fit within the overall "program" of the game and describe how it could be reused throughout the game.

Invite each group to share their function with the class.

Next, introduce My Blocks in Blocks, explaining that this is where learners can create their own reusable functions.

Demonstrate Marty's Walk Forward command several times, encouraging learners to observe the individual movements that make up a single walking action.

Learners should then open the Marty Controller and repeatedly use the walk command, slowing the movement if necessary. Challenge groups to identify the sequence of individual actions that combine to create a walk and discuss how these could be grouped into a single reusable function.

Allow time for learners to compare their ideas before discussing the sequence together.

Time for practice

Next, ask learners to investigate the Kick action. Encourage them to watch the movement several times and identify each step in the sequence. They should pay particular attention to the timing of movements and notice where actions happen one after another or at the same time.

Cool down

Bring the class back together and invite groups to demonstrate their work, explaining how their functions operate and why they structured them in that way. Encourage classmates to ask questions and compare different approaches.

Use the following questions to support discussion:

• Would you use functions every time you write code? Why or why not?
• What are the benefits of using functions?
• If your program contained a bug, would functions make it easier or harder to find the problem? Why?
• Can you think of other situations where repeating the same instructions would be useful?

Finish with your usual end-of-lesson routines before asking learners to log off their devices and tidy away their equipment.