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75 lines
3.6 KiB
Markdown
75 lines
3.6 KiB
Markdown
---
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id: php-numbers
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title: "PHP Numbers"
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category: "Programming_Language"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["is_int", "is_float", "NAN", "PHP 숫자"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.9
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created_at: 2026-07-04
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updated_at: 2026-07-04
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review_reason: ""
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merge_history: []
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tags: ["php", "programming", "w3schools", "numbers"]
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raw_sources: ["https://www.w3schools.com/php/php_numbers.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[PHP Numbers]]
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## 🎯 한 줄 통찰 (One-line insight)
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`4 * 2.5` results in a FLOAT (10.0), not an integer, even though the mathematical result is a whole number — PHP's rule is that if ANY operand in an arithmetic expression is a float, the result is always stored as float, regardless of whether the value happens to be whole. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Three numeric types** — Integer, Float, Numeric Strings; plus Infinity and NaN as special number-related values. [S1]
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- **`is_int()` / `is_float()`** — type checks. [S1]
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- **Integer range** — platform-dependent (32-bit: ±2,147,483,647; 64-bit: much larger); overflow silently becomes a float. [S1]
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- **Integer notations** — decimal, hex (`0x`), octal (`0`), binary (`0b`). [S1]
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- **`PHP_INT_MAX` / `PHP_INT_MIN` / `PHP_INT_SIZE`** — predefined integer limit constants. [S1]
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- **`PHP_FLOAT_MAX` / `MIN` / `DIG` / `EPSILON`** (PHP 7.2+) — predefined float precision constants. [S1]
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- **`is_finite()` / `is_infinite()`** — range checks against platform float limits. [S1]
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- **`NAN`** ("Not A Number") — returned by invalid math operations; checked via `is_nan()`. [S1]
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- **`is_numeric()`** — true for both actual numbers AND numeric strings (e.g., `"5985"`). [S1]
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- **`intval()`** — extracts the integer value from a float or numeric-leading string. [S1]
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## 📖 세부 내용 (Details)
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- Float contagion rule: `4 * 2.5` is 10, but stored as float because one operand (2.5) is a float. [S1]
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- Invalid math yields NAN: `$x = acos(8); var_dump($x); var_dump(is_nan($x)); // true`. [S1]
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- Numeric string check: `$x = "59.85" + 100; var_dump(is_numeric($x)); // true (arithmetic result)`. [S1]
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- intval on string: `$x = "23465.768"; echo intval($x); // 23465`. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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- **부동소수점 전염 규칙**: 연산 결과가 정수 값이어도 피연산자 중 하나가 float이면 결과 타입은 항상 float이 된다는 점이 명시적으로 강조됨. [S1]
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## 🛠️ 적용 사례 (Applied in summary)
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현재 발견된 실제 적용 사례가 없습니다 — is_numeric()으로 사용자 입력이 숫자 형태인지 검증하는 것이 폼 처리의 실전 패턴이다. [S1]
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## 💻 코드 패턴 (Code patterns)
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Float contagion in arithmetic (PHP):
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```php
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$result = 4 * 2.5;
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var_dump($result); // float(10) — not int, because 2.5 is a float
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```
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.90
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[PHP Tutorial]]
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- **관련 개념:** [[PHP Data Types]], [[PHP Casting]], [[PHP Math]]
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- **참조 맥락:** 숫자 타입의 세부 규칙 — 캐스팅(Casting)/수학함수(Math) 챕터로 이어짐.
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## 📚 출처 (Sources)
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- [S1] W3Schools — PHP Numbers — https://www.w3schools.com/php/php_numbers.asp
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## 📝 변경 이력 (Change history)
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- 2026-07-04: Initial draft synthesized from the W3Schools "PHP Numbers" page (Astra wiki-curation, P-Reinforce v3.1 format).
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