---
id: csharp-syntax
title: "C# Syntax"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["using System", "namespace class Main", "C# 문법"]
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: ["csharp", "programming-language", "w3schools", "syntax"]
raw_sources: ["https://www.w3schools.com/cs/cs_syntax.php"]
applied_in: []
github_commit: ""
---

# [[CSharp Syntax]]

## 🎯 한 줄 통찰 (One-line insight)
C# mandates that EVERY line of executable code live inside a `class` — there is no C-style bare top-level `int main()`, no C++-style free function outside any class — which means C#'s minimal program has a mandatory extra nesting layer (`namespace` → `class` → `Main` method) that neither C nor C++ required, and the tutorial explicitly flags one specific Java-vs-C# difference unprompted: unlike Java, the C# filename does NOT have to match the class name (even though convention usually makes them match anyway). [S1]

## 🧠 핵심 개념 (Core concepts)
- **`using System;`** — imports the System namespace, enabling unqualified use of its classes (e.g. `Console` instead of `System.Console`). [S1]
- **`namespace`** — a container for classes and other namespaces, used to organize code. [S1]
- **`class`** — a container for data and methods; ALL executable C# code must be inside a class, with no exception (unlike C's free-standing `main()` or C++'s optional free functions). [S1]
- **Curly braces `{}`** — mark the beginning/end of every code block (namespace body, class body, method body). [S1]
- **`Main` method** — the entry point; code inside its braces is what actually executes when the program runs. [S1]
- **`Console.WriteLine()`** — a method of the `Console` class (part of the `System` namespace) used to print text; omitting `using System;` requires the fully-qualified `System.Console.WriteLine()` instead. [S1]
- **Semicolons mandatory** — every C# statement ends with `;`. [S1]
- **Case-sensitivity** — `MyClass` and `myclass` are distinct identifiers. [S1]
- **Filename vs. class name** — unlike Java (where the public class name MUST match the filename), C# does not enforce this; matching them is convention only, and the saved file must end in `.cs`. [S1]

## 📖 세부 내용 (Details)
- Full annotated example, line by line: `using System;` (namespace import) → blank line (ignored whitespace, used for readability) → `namespace HelloWorld` (organizational container) → `{` (block start) → `class Program` (mandatory class wrapper) → `static void Main(string[] args)` (entry point, keywords deferred to later chapters) → `Console.WriteLine("Hello World!");` (the actual output statement). [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **모든 실행 코드가 반드시 class 안에 있어야 함**: C는 최상위 함수(`int main()`)를, C++는 클래스 밖의 자유 함수(free function)도 허용했지만, C#은 실행되는 모든 코드 줄이 반드시 class 내부에 있어야 한다는 제약이 명시적으로 확인됨 — namespace→class→Main이라는 필수 3중 중첩 구조. [S1]
- **파일명과 클래스명 일치가 Java와 달리 강제되지 않음**: 원문이 직접 "Unlike Java, the name of the C# file does not have to match the class name"이라고 명시 — Java는 public 클래스명과 파일명이 반드시 일치해야 하는 반면, C#은 관례일 뿐 강제 규칙이 아님이 확인됨. [S1]

## 🛠️ 적용 사례 (Applied in summary)
이전 챕터(Get Started)에서 등장한 동일한 Hello World 보일러플레이트를 한 줄씩 분해 설명하는 것이 이번 챕터의 실전 활용 사례로 제시됨. [S1]

## 💻 코드 패턴 (Code patterns)
Minimal C# program structure — namespace/class/Main nesting is mandatory (C#):
```csharp
using System;
namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}
```

## ✅ 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:** [[CSharp Get Started]], [[CSharp Output]], [[Java Intro]], [[CPP Namespaces]]
- **참조 맥락:** Basics 섹션 — Output 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — C# Syntax — https://www.w3schools.com/cs/cs_syntax.php

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