Creating Robust Programs
Defensive design means anticipating how users might break your program and protecting against it. Smart programmers know that users will inevitably enter unexpected data, so you need input validation to catch problems before they crash your system.
Input validation includes several types of checks: range checks (ensuring numbers fall within acceptable limits), type checks (confirming data is the right format), length checks (preventing overly long inputs), presence checks (ensuring required fields aren't empty), and format checks (validating email addresses or phone numbers).
Testing is crucial for catching errors before users do. Syntax errors prevent your code from running at all, while logic errors let the program run but produce wrong results. Use normal data (typical inputs), boundary data (extreme but valid values), and invalid data (completely wrong inputs) to thoroughly test your programs.
Pro Tip: Always test with data you don't expect – that's where most programs break!