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Custom Block Parameters Resetting to Zero - Understanding Variable Scope

💡 Struggling with custom block parameters and variable scope issues? 🚀 Get Expert Help

CH

CodeHelper92

Posted on July 28, 2025 • Intermediate

🔧 Custom Block Parameter Issues

I’m having a weird problem with my custom block parameters. They seem to randomly reset to zero even when I set them to specific numbers and there’s no code that should reset them.

Sometimes the parameters reset outside of the custom block, and sometimes they reset while the function is running! Here’s the code I’m using:

wait until <mouse down?>
wait until <not <mouse down?>>
around(x position)(43)(y position)(32)

And my custom block definition:

define around(xpos)(xrequire)(ypos)(yrequire)
if <<([abs v] of ((xpos) - (xrequire))) < [3]>> and <<([abs v] of ((ypos) - (yrequire))) < [3]>> then
// rest of the code
end

Has anyone else experienced this? The red blocks in my project might be related, but I’m not sure what’s causing this behavior. 🤔

SP

ScratchPro_Expert

Replied 25 minutes later • ⭐ Best Answer

Great question @CodeHelper92! This is actually a very common misunderstanding about how custom block parameters work in Scratch. Let me explain what’s happening and how to fix it:

🎯 Understanding Parameter Scope

The issue you’re experiencing isn’t actually parameters “resetting” - it’s about variable scope. Here’s what’s happening:

flowchart TD A[🚀 Main Script] --> B[Call Custom Block] B --> C[Parameters Available Inside Block] C --> D[Block Execution Completes] D --> E[Parameters No Longer Exist] E --> F[❌ Trying to Access Parameters Outside Block] G[📝 Solution: Use Regular Variables] --> H[Create Global Variables] H --> I[Set Variables Before Calling Block] I --> J[Use Variables Inside Block] J --> K[✅ Variables Accessible Everywhere] style A fill:#e1f5fe style C fill:#e8f5e8 style E fill:#ffebee style F fill:#ffcdd2 style K fill:#e8f5e8

🔍 The Root Problem

Custom block parameters in Scratch have local scope - they only exist while the custom block is running. Once the block finishes, those parameters disappear completely.

What you’re seeing:

  • Parameters work fine inside the custom block
  • Parameters appear as “zero” or undefined outside the custom block
  • This isn’t a bug - it’s how Scratch is designed to work!

✅ Solution 1: Use Global Variables

Instead of trying to access parameters outside the block, use regular variables:

    when flag clicked
set [current x v] to (x position)
set [target x v] to [43]
set [current y v] to (y position)
set [target y v] to [32]
around
  
    define around
if <<([abs v] of ((current x) - (target x))) < [3]>> and <<([abs v] of ((current y) - (target y))) < [3]>> then
// your code here
end

✅ Solution 2: Return Values from Custom Blocks

Use reporter blocks to get information out of your custom blocks:

    define check distance (x1) (y1) (x2) (y2)
set [distance result v] to ([sqrt v] of (((x1) - (x2)) * ((x1) - (x2))) + (((y1) - (y2)) * ((y1) - (y2))))

// In your main script:
if <(check distance (x position) (y position) (43) (32)) < [5]> then
// do something
end

✅ Solution 3: Proper Parameter Usage

If you want to keep using parameters, make sure all logic stays inside the custom block:

    define around and do action (xpos) (xrequire) (ypos) (yrequire)
if <<([abs v] of ((xpos) - (xrequire))) < [3]>> and <<([abs v] of ((ypos) - (yrequire))) < [3]>> then
// do all your actions here, inside the block
say [Close enough!] for (2) seconds
change [score v] by [10]
// etc.
end

// Call it like this:
around and do action (x position) (43) (y position) (32)

🚨 Common Mistakes to Avoid

  • Don’t try to use custom block parameters in separate scripts
  • Don’t expect parameters to persist after the block finishes
  • Don’t use parameters as global storage - use variables instead

🎮 Best Practices

  • Use parameters for input to your custom blocks
  • Use global variables for data that needs to persist
  • Use reporter blocks to output results from custom blocks
  • Keep all parameter-dependent logic inside the custom block

Hope this clears up the confusion! The behavior you’re seeing is completely normal - it’s just how variable scope works in programming. 😊

CH

CodeHelper92

Replied 45 minutes later

@ScratchPro_Expert This makes so much sense now! 🤯 I was trying to use the parameters like global variables.

I switched to using regular variables and now everything works perfectly. Thank you for the detailed explanation!

DT

DebugMaster_Tom

Replied 1 hour later

Great explanation @ScratchPro_Expert! 👏 I’d like to add a debugging tip for anyone facing similar issues:

🔍 How to Debug Parameter Issues:

  • Add say blocks inside your custom block to check parameter values
  • Use the debugger to step through your code
  • Remember: if you see “0” or empty values, check if you’re accessing parameters outside their scope

This scope concept applies to many programming languages, so understanding it in Scratch will help you later! 🚀

VB

Vibelf_Community

Pinned Message • Moderator

🎓 Master Advanced Programming Concepts

Excellent discussion about variable scope! For those wanting to dive deeper into programming concepts like:

  • 🔄 Variable scope and lifetime
  • 📦 Function parameters and return values
  • 🏗️ Code organization and structure
  • 🐛 Debugging techniques and best practices

📚 Related Topics

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