Creating Global Variables in Scratch: A Simple Explanation

📚 What are Global Variables in Scratch?

Global variables in Scratch are like shared information buckets that all parts of your project can access and change. Think of it as a message board where all your sprites and scripts can read and write information. This is super handy when you need different parts of your program to communicate or share data, such as keeping track of the score in a game or managing a countdown timer that affects all sprites.

🧑‍🏫 Objectives

• 🎯 Students will be able to define what a global variable is.
• 💻 Students will be able to create global variables in Scratch.
• 🤝 Students will be able to use global variables to make sprites interact.

⚙️ Materials

• 💻 Computers with internet access.
• 🌐 Scratch website access (scratch.mit.edu).
• 📝 Worksheet (provided below).

⏰ Warm-up (5 mins): Variable Brainstorm

Ask students: What are some things we might want to keep track of in a game or animation? (e.g., score, time, lives, level)

📝 Main Instruction

1. ➕ Creating a Global Variable

   • ➡️ Open Scratch and start a new project.
   • ➕ Go to the 'Variables' category in the code blocks palette.
   • 🆕 Click on 'Make a Variable'.
   • ✍️ Name your variable (e.g., 'score', 'timer'). Important: Ensure 'For all sprites' is selected to make it a global variable.
   • ✅ Click 'OK'. You will now see blocks for setting, changing, showing, and hiding your variable.

2. 🕹️ Using Global Variables

   • 🧱 Add a sprite to your project.
   • 🏁 Use the 'when green flag clicked' block to start your script.
   • ⚙️ Use the 'set [variable] to [value]' block to initialize the variable at the start of the game (e.g., set 'score' to 0).
   • 🔄 Use the 'change [variable] by [value]' block to update the variable (e.g., change 'score' by 10 when the sprite touches another sprite).
   • 👁️ Use the 'show variable [variable]' block to display the variable on the stage.

3. 🤝 Example: Score Tracker

   • 👾 Create two sprites: a player and a target.
   • 🧱 When the player touches the target, change the 'score' variable by 1.
   • 💬 Display the 'score' variable on the stage so the player can see their score increasing.

📝 Assessment

• ❓ Question 1: What is a global variable in Scratch?
• ❓ Question 2: How do you create a global variable instead of a local variable?
• ❓ Question 3: Give an example of when you would use a global variable.