The Order of the Off-By-One

< versus <=. Index zero versus index one. The smallest bugs cause the strangest failures.

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Choose a format Metal challenge coin Coming soon 1.75" antique-bronze coin with a 3D high-relief front, raised rim lettering and a beaded edge. Ships in a clear capsule with a backing card. Plastic challenge coin Coming soon 1.75" soft PVC (rubber) coin with 2-3 levels of relief, painted in antique-bronze tones. Lighter and lower-cost than metal. Ships in a clear capsule with a backing card.Available once the artwork is finished. Die-cut vinyl sticker Coming soon 3" die-cut vinyl sticker of the coin artwork with a UV- and water-resistant laminate. Laptop and water-bottle grade.Available once the artwork is finished.

Physical coins and stickers are coming soon. Until then, you can email this coin for free.

Meaning

< versus <=. Index zero versus index one. The smallest bugs cause the strangest failures.

Design

Front (Obverse)

Top rim: THE ORDER OF THE OFF-BY-ONE
Bottom rim: BOUNDARY CONDITIONS DIVISION
Center: Eleven knights crowd around a round table built for ten. Their seats are numbered 0 through 10, and the last knight balances on the edge of the table.

Back (Reverse)

A scroll inscribed "THERE ARE 2 HARD PROBLEMS: NAMING THINGS, CACHE INVALIDATION, AND OFF-BY-ONE ERRORS".

Finish & Style

Antique bronze challenge coin, ~1.75" diameter, high-relief center scene, raised rim lettering, beaded outer edge. Matches the existing ITChallengeCoins series.

How to Earn It

Find and fix an off-by-one bug in production code.
Bonus if it was a fencepost error in a date range, pagination or array loop.
Or write the unit tests that check the boundary cases nobody else thought of.

Citation

For counting carefully, starting from zero, and stopping exactly where it ends.