Technical mental model

Input/output code looks simple until malformed data, locale differences, and buffering behavior interact. Robust IO design is mostly about validation and explicit state handling.

Key low-level points:

• Formatted IO requires exact type/format alignment to remain defined and portable.
• Stream buffering changes when data is physically visible and when it is flushed.
• Input parsing should separate acquisition from validation to keep logic testable.

Equations and constraints that drive decisions

Observed IO throughput:

Where:

• $R$: bytes per second
• $B$: bytes processed
• $t$: elapsed time

Implementation walkthrough

Capture line input first (fgets style), then parse tokens with explicit checks.

Validate count and range for every parsed field before use.

Handle EOF and parse failures as expected runtime states, not exceptional crashes.

Structure IO code so prompts, parse, and business logic remain separate.

Validation and debugging checklist

Never trust scanf path without checking return value count.

Do not mix numeric and line-based input without buffer normalization.

Treat parse failures as data-quality issues and provide recovery path.

Explicitly test malformed and partial inputs.

High-quality IO code is deterministic under bad data, not only under happy-path input.