2nd/10_Wiki/Topic_Programming/Topic_CSharp/CSharp_User_Input.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
csharp-user-input	C# User Input	Programming_Language	draft	conceptual		Console.ReadLine C# 사용자 입력		B	0.85	2026-07-04	2026-07-04			csharp programming-language w3schools user-input	https://www.w3schools.com/cs/cs_user_input.php

CSharp User Input

🎯 한 줄 통찰 (One-line insight)

This chapter is the exact payoff the Type Casting chapter promised — "take a look at the next chapter, when working with user input, to see an example of this [conversion]" — and it delivers precisely that: Console.ReadLine() ALWAYS returns a string, full stop, unlike C++'s cin >> or C's scanf() which can read directly into a typed variable (int, double, etc.); trying int age = Console.ReadLine(); is a compile error ("Cannot implicitly convert type 'string' to 'int'"), forcing every numeric input in C# through an explicit Convert.ToInt32() (or similar) call, with a runtime System.FormatException risk if the user types non-numeric text — a failure mode C's scanf() doesn't raise as an exception (it silently fails to parse) and C++'s cin >> handles via the stream-error-state mechanism already documented in [[CPP Input Validation]]. [S1]

🧠 핵심 개념 (Core concepts)

• Console.ReadLine() — reads a line of keyboard input and returns it as a string; the counterpart to Console.WriteLine(). [S1]
• Always returns string — there is no direct "read an int" or "read a double" variant; every input arrives as text first. [S1]
• Implicit conversion is illegal — int age = Console.ReadLine(); fails at compile time with "Cannot implicitly convert type 'string' to 'int'". [S1]
• Convert.ToInt32() (and siblings) — the explicit conversion method required to turn the string input into a usable numeric type, directly reusing the Convert.To* family from the Type Casting chapter. [S1]
• Runtime parse failure — if the user enters non-numeric text where a number is expected, Convert.ToInt32() throws a System.FormatException ("Input string was not in a correct format.") — a RUNTIME exception, not a compile error; full handling deferred to a later Exceptions chapter. [S1]

📖 세부 내용 (Details)

• Basic string input: Console.WriteLine("Enter username:"); string userName = Console.ReadLine(); Console.WriteLine("Username is: " + userName);. [S1]
• Failing numeric input attempt: Console.WriteLine("Enter your age:"); int age = Console.ReadLine(); Console.WriteLine("Your age is: " + age); → compile error. [S1]
• Fixed with explicit conversion: Console.WriteLine("Enter your age:"); int age = Convert.ToInt32(Console.ReadLine()); Console.WriteLine("Your age is: " + age);. [S1]

⚖️ 모순 및 업데이트 (Contradictions & updates)

• Type Casting 챕터의 예고가 이 챕터에서 실현됨: Type Casting 챕터가 "다음 챕터(사용자 입력)에서 왜 변환이 필요한지 확인하라"고 예고했는데, 이번 챕터가 정확히 그 이유(ReadLine()이 항상 string만 반환)와 해결책(Convert.ToInt32())을 보여준다는 점이 확인됨. [S1]
• C/C++의 typed 입력과 달리 항상 string으로만 들어옴: C의 scanf()나 C++의 cin >>는 변수 타입에 맞춰 직접 파싱해 읽을 수 있었지만, C#의 Console.ReadLine()은 항상 string만 반환하므로 숫자가 필요하면 반드시 Convert.ToInt32() 같은 명시적 변환을 거쳐야 한다는 점이 확인됨 — 컴파일 타임 에러(암묵적 변환 금지)로 이를 강제함. [S1]

🛠️ 적용 사례 (Applied in summary)

사용자로부터 나이를 입력받아 Convert.ToInt32(Console.ReadLine())으로 정수로 변환한 뒤 출력하는 예제가 원문에서 직접 실전 활용 사례로 제시됨. [S1]

💻 코드 패턴 (Code patterns)

Console.ReadLine() always returns string — explicit conversion required for numbers (C#):

Console.WriteLine("Enter your age:");
int age = Convert.ToInt32(Console.ReadLine());  // explicit conversion required
Console.WriteLine("Your age is: " + age);
// Non-numeric input throws System.FormatException at runtime

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.85
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: C# Tutorial
• 관련 개념: CSharp Type Casting, CSharp Enums, CSharp Exceptions, CPP Input Validation
• 참조 맥락: User Input 섹션의 유일 챕터 — Exceptions 섹션으로 이어짐.

📚 출처 (Sources)

• [S1] W3Schools — C# User Input — https://www.w3schools.com/cs/cs_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).