---
id: php-numbers
title: "PHP Numbers"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["is_int", "is_float", "NAN", "PHP 숫자"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["php", "programming", "w3schools", "numbers"]
raw_sources: ["https://www.w3schools.com/php/php_numbers.asp"]
applied_in: []
github_commit: ""
---

# [[PHP Numbers]]

## 🎯 한 줄 통찰 (One-line insight)
`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]

## 🧠 핵심 개념 (Core concepts)
- **Three numeric types** — Integer, Float, Numeric Strings; plus Infinity and NaN as special number-related values. [S1]
- **`is_int()` / `is_float()`** — type checks. [S1]
- **Integer range** — platform-dependent (32-bit: ±2,147,483,647; 64-bit: much larger); overflow silently becomes a float. [S1]
- **Integer notations** — decimal, hex (`0x`), octal (`0`), binary (`0b`). [S1]
- **`PHP_INT_MAX` / `PHP_INT_MIN` / `PHP_INT_SIZE`** — predefined integer limit constants. [S1]
- **`PHP_FLOAT_MAX` / `MIN` / `DIG` / `EPSILON`** (PHP 7.2+) — predefined float precision constants. [S1]
- **`is_finite()` / `is_infinite()`** — range checks against platform float limits. [S1]
- **`NAN`** ("Not A Number") — returned by invalid math operations; checked via `is_nan()`. [S1]
- **`is_numeric()`** — true for both actual numbers AND numeric strings (e.g., `"5985"`). [S1]
- **`intval()`** — extracts the integer value from a float or numeric-leading string. [S1]

## 📖 세부 내용 (Details)
- Float contagion rule: `4 * 2.5` is 10, but stored as float because one operand (2.5) is a float. [S1]
- Invalid math yields NAN: `$x = acos(8); var_dump($x); var_dump(is_nan($x)); // true`. [S1]
- Numeric string check: `$x = "59.85" + 100; var_dump(is_numeric($x)); // true (arithmetic result)`. [S1]
- intval on string: `$x = "23465.768"; echo intval($x); // 23465`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **부동소수점 전염 규칙**: 연산 결과가 정수 값이어도 피연산자 중 하나가 float이면 결과 타입은 항상 float이 된다는 점이 명시적으로 강조됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — is_numeric()으로 사용자 입력이 숫자 형태인지 검증하는 것이 폼 처리의 실전 패턴이다. [S1]

## 💻 코드 패턴 (Code patterns)
Float contagion in arithmetic (PHP):
```php
$result = 4 * 2.5;
var_dump($result); // float(10) — not int, because 2.5 is a float
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[PHP Tutorial]]
- **관련 개념:** [[PHP Data Types]], [[PHP Casting]], [[PHP Math]]
- **참조 맥락:** 숫자 타입의 세부 규칙 — 캐스팅(Casting)/수학함수(Math) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — PHP Numbers — https://www.w3schools.com/php/php_numbers.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "PHP Numbers" page (Astra wiki-curation, P-Reinforce v3.1 format).
