2nd/10_Wiki/Topic_Programming/Topic_C/C_User_Input.md

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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-user-input	C User Input	Programming_Language	draft	conceptual		scanf function fgets function C 사용자 입력		B	0.87	2026-07-04	2026-07-04			c programming-language w3schools user-input scanf fgets	https://www.w3schools.com/c/c_user_input.php

C User Input

🎯 한 줄 통찰 (One-line insight)

scanf("%s", ...) treats WHITESPACE as a terminator — the source's own demonstration types "John Doe" but the program only prints "John," silently dropping everything after the first space — which is exactly why fgets() exists as a SEPARATE tool specifically for multi-word input, meaning the choice between scanf() and fgets() isn't stylistic, it's dictated by whether the expected input could ever contain a space. [S1]

🧠 핵심 개념 (Core concepts)

• scanf(format, &variable) — reads user input matching the given format specifier; requires the & reference operator for basic types (but NOT for strings, since an array name is already a pointer). [S1]
• Multiple inputs in one call — scanf("%d %c", &myNum, &myChar); reads several values matched to their respective format specifiers in order. [S1]
• String input via scanf("%s", name) — no & needed (array name = pointer); requires a large-enough buffer declared in advance (e.g. char firstName[30]). [S1]
• scanf's whitespace-termination limitation — treats spaces/tabs as a terminating character, so it can only capture a SINGLE WORD even if the user types multiple words. [S1]
• fgets(buffer, sizeof(buffer), stdin) — reads a full LINE of text including spaces, the correct tool for multi-word input like a full name. [S1]

📖 세부 내용 (Details)

• Basic numeric input: int myNum; scanf("%d", &myNum);. [S1]
• Multiple inputs in one call: int myNum; char myChar; scanf("%d %c", &myNum, &myChar);. [S1]
• String input demonstrating the space-termination trap: char fullName[30]; scanf("%s", &fullName); // "Type your full name: John Doe" → prints only "Hello John". [S1]
• The fgets() fix for multi-word input: char fullName[30]; fgets(fullName, sizeof(fullName), stdin); // "John Doe" → prints "Hello John Doe". [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• scanf("%s", ...)는 공백에서 끊김: "John Doe"를 입력해도 공백을 종료 문자로 취급해 "John"만 출력된다는 점이 직접 예제로 증명되며, 여러 단어를 받으려면 fgets()를 써야 한다는 대안이 명확히 제시됨. [S1]

🛠️ 적용 사례 (Applied in summary)

사용자의 전체 이름(공백 포함)을 정확히 입력받기 위해 scanf() 대신 fgets()를 사용하는 예제가 원문에서 직접 실전 활용 사례로 제시됨. [S1]

💻 코드 패턴 (Code patterns)

Reading a full line of text (including spaces) with fgets() instead of scanf() (C):

char fullName[30];
printf("Type your full name: \n");
fgets(fullName, sizeof(fullName), stdin);
printf("Hello %s", fullName); // "John Doe" prints in full

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.87
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: C Tutorial
• 관련 개념: C Scope, C Do While Loop, C Date Time
• 참조 맥락: 사용자 입력 — 날짜와 시간(Date Time) 챕터로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — C User Input — https://www.w3schools.com/c/c_user_input.php

📝 변경 이력 (Change history)

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