C# Syntax

Program Structure

A C# source file declares a namespace that contains classes. A class holds members: fields, properties, and methods. Execution starts in a Main method.

Using Directives

The using directive imports a namespace so you can use its types without a full prefix.

using System;                 // Console, Math
using System.Collections.Generic; // List<T>, Dictionary<TKey,TValue>

Namespace

A namespace groups related types and prevents name collisions across assemblies.

namespace SageCode.Demo
{
    // types go here
}

Class

A class is a blueprint for objects. It contains fields, properties, and methods.

class Program
{
    // members go here
}

Main Method

Main is the entry point. The runtime calls it when the program starts.

static void Main(string[] args)  // static: can run without an instance
{
    Console.WriteLine("Hello, World!"); // write one line to the console
}

Code Elements

Statements

Every statement ends with a semicolon ;. Typical statements: declarations, assignments, method calls.

int total = 0;              // declaration + assignment
total = total + 2;          // assignment statement
Console.WriteLine(total);   // method call statement

Blocks

Braces { } group statements into a block. A block defines scope: variables declared inside are not visible outside.

if (total > 0)
{
    int doubled = total * 2;  // 'doubled' lives only inside this block
    Console.WriteLine(doubled);
}
// 'doubled' is not visible here — the block defined its scope

Comments

Comments are for humans — they document intent and are ignored by the compiler. Write why, not what the code obviously does.

• // single-line comment
• /* ... */ multi-line comment
• /// XML documentation comment

// single-line comment
/* multi-line
   comment */
/// <summary>Computes the sum of two integers.</summary>
static int Add(int a, int b) => a + b;

Operators

Operator Table

Common Pitfalls

Missing Semicolon

Forgetting the terminal semicolon is the most frequent compile error in beginner code.

Case Sensitivity

Main and main are different identifiers. Class names use PascalCase; local variables use camelCase.

Uninitialized Locals

Local variables must be assigned before first use; the compiler rejects reads of uninitialized variables.