Which principle specifies that inputs should be checked for type and range constraints?

• A. Validate all inputs
• B. Enforce type and range constraints
• C. Reject invalid data early
• D. Provide safe error messages

Answer: (B)

The main idea here is ensuring that inputs match what the program expects by checking their type and their value ranges. Enforcing type and range constraints means you explicitly require inputs to be the correct data type (for example, a number, not a string) and within allowed bounds (like a score between 0 and 100). This directly prevents a lot of downstream problems, such as type errors, incorrect calculations, or security issues caused by out-of-range or malformed data.

This option is the most precise way to describe the practice of validating inputs against their expected characteristics. While “validate all inputs” is a valid broader goal, it doesn’t specify which checks to perform. “Reject invalid data early” is good guidance but focuses on timing rather than the exact checks. “Provide safe error messages” is about how you report problems, not about preventing them in the first place.