---
id: c-user-input
title: "C User Input"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["scanf function", "fgets function", "C 사용자 입력"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.87
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["c", "programming-language", "w3schools", "user-input", "scanf", "fgets"]
raw_sources: ["https://www.w3schools.com/c/c_user_input.php"]
applied_in: []
github_commit: ""
---

# [[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):
```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).