Rules for Creating Functions in Scratch

📚 Understanding Functions (My Blocks) in Scratch

In Scratch, 'My Blocks' allow you to create custom commands, similar to functions in other programming languages. They help organize code, make it reusable, and improve readability. Here's a comprehensive guide to the rules for creating and using them effectively:

📜 History and Background

The concept of custom blocks was introduced to Scratch to enable more advanced programming techniques and to allow users to abstract complex tasks into simpler, reusable components. This feature significantly enhances the educational value of Scratch by introducing fundamental programming concepts in an accessible way.

🔑 Key Principles for Creating Functions in Scratch

• 🧱 Naming Conventions: Choose descriptive names for your blocks. A good name clearly indicates what the block does (e.g., 'move_to_random_position' is better than 'block1').
• ✏️ Input Parameters: Determine what inputs your block needs. Scratch allows you to define input parameters (numbers, text, or boolean values) that the block will use when executed.
• ⚙️ No Direct Output: Scratch blocks don't directly return values like functions in some languages. Instead, they modify variables or control the behavior of sprites.
• 🔁 Reusability: Design blocks to be reusable in different parts of your project. Avoid hardcoding values that might change.
• 🌎 Scope: Blocks operate within the scope of the sprite or globally. Consider where the block will be used and define it accordingly.
• 🧠 Clarity: Keep blocks concise and focused on a single task. If a block becomes too long or complex, consider breaking it down into smaller blocks.
• 💡 Documentation: Add comments to your block definitions to explain what they do, especially if they perform complex calculations or interactions.

👨‍🏫 Real-world Examples

Let's look at some practical examples of creating functions in Scratch:

1. Drawing a Square: Create a block that draws a square of a specified size.

Steps:

1. Create a new block named 'draw_square' with an input parameter 'side_length'.
2. Inside the block definition, use the 'move' and 'turn' blocks to draw the four sides of the square.

Scratch Code:

define draw_square (side_length)
 repeat (4)
 move (side_length) steps
 turn right (90) degrees
 end

2. Moving to a Random Position: Create a block that moves a sprite to a random x and y position on the stage.

Steps:

1. Create a new block named 'move_to_random_position'.
2. Inside the block definition, use the 'go to x: () y: ()' block with random number inputs.

Scratch Code:

define move_to_random_position
 go to x: (pick random (-240) to (240)) y: (pick random (-180) to (180))

🧮 Example with LaTeX

Here's how you can define a function to calculate the area of a rectangle, although Scratch doesn't directly support returning values. You would typically store the result in a variable.

Let $A$ be the area, $l$ be the length, and $w$ be the width. The formula is:

$A = l \times w$

In Scratch, you can create a block to set a variable to this value:

define calculate_rectangle_area (length) (width)
 set [area] to (length * width)

📝 Conclusion

Understanding and using functions (My Blocks) in Scratch is crucial for creating more organized, efficient, and readable code. By following these rules and guidelines, you can effectively leverage functions to enhance your Scratch projects and introduce fundamental programming concepts.