2nd/10_Wiki/Dev/Topic_C/C_Functions_Recursion.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
c-functions-recursion	C Recursion	Programming_Language	draft	conceptual		recursive function base case factorial recursion C 재귀		B	0.86	2026-07-04	2026-07-04			c programming-language w3schools functions recursion	https://www.w3schools.com/c/c_functions_recursion.php

C Recursion

🎯 한 줄 통찰 (One-line insight)

Every recursive function in the source's examples relies on a single structural guarantee: the function ONLY calls itself when a shrinking condition still holds (k > 0, n > 0, n > 1) and returns a plain value OTHERWISE — the source's own warning that recursion "can be quite easy to slip into writing a function which never terminates" is really pointing at what happens if that shrinking condition is missing or wrong, not at recursion itself being inherently risky. [S1]

🧠 핵심 개념 (Core concepts)

• Recursion — a function calling ITSELF, breaking a complex problem into smaller instances of the same problem. [S1]
• Base case — the condition under which the function STOPS calling itself and returns directly (e.g. k > 0 becoming false), essential for termination. [S1]
• Unwinding accumulation — each recursive call's return combines its own contribution with the result of the smaller sub-call (return k + sum(k - 1);), building up the final answer as calls return in reverse order. [S1]
• Risk of non-termination or excess resource use — without a solid base case, recursion can run forever or exhaust memory/processor time. [S1]

📖 세부 내용 (Details)

• Summing 1 to 10 via recursion: int sum(int k) { if (k > 0) { return k + sum(k - 1); } else { return 0; } } — unfolds as 10 + (9 + (8 + ... + sum(0))). [S1]
• Countdown via recursion: void countdown(int n) { if (n > 0) { printf("%d ", n); countdown(n - 1); } } — stops calling itself once n reaches 0. [S1]
• Factorial via recursion: int factorial(int n) { if (n > 1) { return n * factorial(n - 1); } else { return 1; } } — factorial(5) = 5×4×3×2×1 = 120; by definition 0! is also 1. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• 재귀의 종료 조건이 핵심 위험 요소: 종료되지 않는 함수나 과도한 메모리/CPU를 쓰는 함수를 실수로 작성하기 쉽다는 경고가 있지만, 이는 결국 축소 조건(base case)이 없거나 잘못됐을 때 발생하는 문제임이 예제들에서 공통적으로 드러남. [S1]

🛠️ 적용 사례 (Applied in summary)

5의 팩토리얼(5×4×3×2×1=120)을 재귀로 계산하는 예제가 원문에서 직접 실전 활용 사례로 제시됨. [S1]

💻 코드 패턴 (Code patterns)

A recursive function with a clear base case that guarantees termination (C):

int factorial(int n) {
  if (n > 1) {
    return n * factorial(n - 1);
  } else {
    return 1; // base case
  }
}

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.86
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: C Tutorial
• 관련 개념: C Functions Parameters, C Memory Allocate, C Functions Pointers
• 참조 맥락: 재귀 — 함수 포인터(Functions Pointers) 챕터로 이어짐, 스택 메모리(Memory Allocate 챕터의 스택 오버플로우 개념)와 연결.

📚 출처 (Sources)

• [S1] W3Schools — C Recursion — https://www.w3schools.com/c/c_functions_recursion.php

📝 변경 이력 (Change history)

• 2026-07-04: Initial draft synthesized from the W3Schools "C Recursion" page (Astra wiki-curation, P-Reinforce v3.1 format).