Debugging with Error Messages

Types of Errors

• Syntax Errors
  • Program won't start running.
  • Caused by typos, incorrect function usage, or misuse of loops.
• Runtime Errors
  • Program starts running but crashes.
• Logic Errors
  • Program runs without crashing but doesn't produce the expected result.

Understanding Error Messages

• Error messages often arise from syntax or runtime errors.
• They can be cryptic, but systems attempt to make them user-friendly.
• Error messages provide valuable information for debugging.

Example Error Messages

• "Carol crashed into a wall. Error on line 22."
  • Indicates the location and possible cause, e.g., an extra move command.
• "Uncaught Reference Error: 'great steps' is not defined."
  • Suggests a possible typo or undefined variable.
• "Unexpected identifier."
  • Points to potential issues with syntax, like brackets or parentheses.

Extracting Information from Error Messages

• Check if the error message references a function or line number.
• Use any provided hints to aid the debugging process.

Debugging Example: Building a Staircase

1. Initial Error: "Bad input on line 10"
   • Focus on the specified line.
   • Missing semicolon after a while condition.
2. Second Error: "Named term 'right' is not defined."
   • Command 'turn right' not recognized.
   • Solution: Define 'turn right' as three 'turn left' commands.

Key Takeaways

• Error messages help identify where to focus when debugging.
• Provides insights into poorly defined commands or syntax errors.
• Encourages systematic checks using line numbers and function references.

---

Practical Steps for Debugging

• Always check the specific line number referenced in the error message.
• Verify that all functions or commands used are properly defined.
• Utilize error hints to streamline the debugging process.

Your Turn:

• Apply these techniques to debug your own code effectively.