CSV Validator — illustrative example

INPUT
CSV schema: id is required; quantity must be a nonnegative integer. Header is record 1.
id,quantity
A1,2
A2,many

RESULT
Structure: two columns per record; required headers present.
Record 3, id A2, quantity "many": fails nonnegative-integer rule.
Record 2, id A1, quantity 2: passes.
Original values retained; one record needs correction.

REVIEW
Validate both file structure and the expected schema. A well-formed CSV can still contain missing fields or values of the wrong type.

This is a teaching example, not a live execution record.