---
id: c-switch
title: "C Switch"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["switch case", "break keyword", "default keyword", "C switch 문"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.86
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["c", "programming-language", "w3schools", "switch"]
raw_sources: ["https://www.w3schools.com/c/c_switch.php"]
applied_in: []
github_commit: ""
---

# [[C Switch]]

## 🎯 한 줄 통찰 (One-line insight)
`break` isn't optional cleanup — without it, C would keep executing every subsequent `case` block regardless of whether it matches, since `switch` on its own only decides WHERE to jump in, not where to stop; the source frames `break` as actively saving execution time by "ignoring" the rest of the switch block once a match is handled, implying that omitting it (fall-through) is a real and easy-to-make mistake in C, unlike languages where each case implicitly breaks. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`switch (expression)`** — evaluates the expression ONCE, then compares it against each `case` value to find a match. [S1]
- **`case x:`** — a candidate value to match against; its code block runs if the switch expression equals `x`. [S1]
- **`break`** — exits the switch block immediately once a matching case has been handled, preventing execution from continuing into subsequent cases. [S1]
- **`default:`** — optional; runs if no case matches; must be the LAST statement in the switch and does not need its own `break`. [S1]

## 📖 세부 내용 (Details)
- Weekday-name lookup via switch: `int day = 4; switch (day) { case 1: printf("Monday"); break; ... case 4: printf("Thursday"); break; ... }` — outputs "Thursday" for day 4. [S1]
- Using default for unmatched cases: `int day = 4; switch (day) { case 6: printf("Today is Saturday"); break; case 7: printf("Today is Sunday"); break; default: printf("Looking forward to the Weekend"); }` — day 4 matches neither case 6 nor 7, so default runs. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **break 생략 시 다음 case로 계속 진행됨**: switch는 일치하는 case를 찾아 진입점만 결정할 뿐, break가 없으면 이후 모든 case의 코드가 계속 실행된다는 점(fall-through)이 암묵적으로 경고됨. [S1]
- **default는 반드시 마지막에 위치**: default 키워드는 switch 블록의 마지막 statement여야 하며 break가 필요 없다는 점이 명시적으로 확인됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
요일 번호(1-7)를 요일 이름으로 변환하는 예제와, 주말이 아닌 요일에 대해 default로 "주말이 기대된다"는 메시지를 출력하는 예제가 원문에서 직접 실전 활용 사례로 제시됨. [S1]

## 💻 코드 패턴 (Code patterns)
Using default to handle any value not matched by an explicit case (C):
```c
int day = 4;
switch (day) {
  case 6:
    printf("Today is Saturday");
    break;
  case 7:
    printf("Today is Sunday");
    break;
  default:
    printf("Looking forward to the Weekend");
}
// Outputs "Looking forward to the Weekend"
```

## ✅ 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 Conditions RealLife]], [[C While Loop]]
- **참조 맥락:** switch 섹션 유일 챕터 — 반복문(Loops) 섹션의 while 루프(While Loop) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C Switch — https://www.w3schools.com/c/c_switch.php

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