Cognitive Scaffold

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MENTAL MODEL · M0261

Off-by-one Error

Off-by-one Error
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Version 1.0.0 · Updated 2026-07-28

CORE DEFINITION

An off-by-one error (OBOE) is an error in counting where the result is one more or one less than it should be due to a mistake in judging boundary conditions. It typically refers to a programming error in which a loop iterates one time too many or one time too few, and is a type of logical error. For example, a programmer might use "less than" instead of "less than or equal to" in a loop comparison, or fail to account for a sequence starting at 0 rather than 1 (as is the case with array indices in many programming languages). This error also occurs in mathematics.

SCAFFOLDING EFFECT

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An off-by-one error (OBOE) is an error in counting where the result is one more or one less than it should be due to a mistake in judging boundary conditions. It typically refers to a programming error in which a loop iterates one time too many or one time too few, and is a type of logical error. For example, a programmer might use "less than" instead of "less than or equal to" in a loop comparison, or fail to account for a sequence starting at 0 rather than 1 (as is the case with array indices in many programming languages). This error also occurs in mathematics.

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In counting, indexing, and boundary handling, a deviation in the starting/ending point (e.g., counting from 0 vs. 1) leads to a result that is off by one. The root cause is confusion between "interval endpoints" and "counting" (the number of posts equals the number of intervals plus one).

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Source support: Explicit

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    zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E5%B7%AE%E4%B8%80%E9%94%99%E8%AF%AFZH · Explicit
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