Write a contract: inputs, result and allowed changes
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A procedure’s interface is the boundary between caller and helper. Its contract states what the caller supplies, what the helper returns, and what changes to the input are permitted. The implementation is how the helper performs the work.
| Contract part | Example: SumMarks |
|---|---|
| Inputs | A nonempty or empty score dataset, a valid Gender value, and a valid numeric field name. |
| Result | The sum of that field for all matching records; zero if no rows match. |
| Data integrity | Do not change marks, IDs or records. |
| Order policy | Preserve the original order, or explicitly document if order may change. |
Replace the method while preserving the promise
If you improve one procedure, every call can benefit without rewriting the main code. But the new version must preserve the agreed input meaning, result and side-effect policy. Returning the same number is insufficient if the new version unexpectedly destroys a carefully sorted deck.
Some tasks depend on the sequence
For a text-search exercise, a pronoun such as He can be associated with a preceding name by a backwards-search rule. In the supplied paragraph, Swaminathan occurs before the later He. Shuffling the word records destroys the “before” relation. Preserve SerialNumber and order when using such a rule.
Nearest preceding name is a simplified course heuristic, not a complete English-language pronoun resolver. A PartOfSpeech label of Noun alone does not prove that a word is a person’s name; apply the rule specified by the task.
Example contract for a text search:
Input: a pronoun position and the ordered words before/after it
Output: a matching name under the stated search rule, or "not found"
Allowed changes: none to words, IDs, or orderA reading-only loop over table rows need not move the rows at all. Card-pile pseudocode makes movement visible; real implementations must still make their data-change promises explicit.
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What is the difference between interface and implementation?
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The interface is the agreement the caller relies on. The implementation is the internal method used to meet it.
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May a faster procedure violate its old order guarantee?
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No. It must preserve the full contract, including allowed changes.
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Why is shuffling word cards dangerous for a backwards search?
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It changes which words come before the pronoun and can change the answer.
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Must every procedure return a useful number?
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No. Some procedures act by updating or rearranging data.