Basic Syntax

Program Structure

A classic C# program consists of using directives, a namespace, a class, and a Main method.

• using directive: Imports a namespace so you don't have to write fully qualified paths
• namespace: A logical container for organizing code and preventing naming conflicts
• class: C# is object-oriented; all code must reside inside a class
• Main method: The program's entry point where execution begins

Example

using System;

namespace MyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");
        }
    }
}

Hello, World!

Statements and Semicolons

Every statement in C# must end with a semicolon ;. The semicolon is a statement terminator that tells the compiler where one instruction ends. A missing semicolon will cause a compilation error.

Example

using System;

namespace StatementDemo
{
    class Program
    {
        static void Main()
        {
            int x = 10;
            int y = 20;
            int sum = x + y;
            Console.WriteLine(sum);
        }
    }
}

30

Code Blocks and Braces

A code block is wrapped in braces { }, grouping multiple statements into a single logical unit. Namespaces, classes, methods, conditionals, and loops all require code blocks. Braces can be nested.

namespace Outer
{
    namespace Inner
    {
        class MyClass
        {
            void MyMethod()
            {
                if (true)
                {
                    Console.WriteLine("nested block");
                }
            }
        }
    }
}

Indentation and Code Style

Good indentation makes code easier to read. The C# community recommends 4 spaces for indentation. There are two common brace styles:

• Allman style: Opening brace on its own line (common in C#)
• K&R style: Opening brace at the end of the previous line

class StyleA
{
    void Method()
    {
        Console.WriteLine("Allman style");
    }
}

class StyleB {
    void Method() {
        Console.WriteLine("K&R style");
    }
}

Tip: Visual Studio uses Allman style by default. What matters most is consistency within a project.

Console Output

Console.Write and Console.WriteLine are used to output text to the console:

• Console.Write: Outputs text without a trailing newline
• Console.WriteLine: Outputs text followed by a newline

Example

using System;

namespace ConsoleDemo
{
    class Program
    {
        static void Main()
        {
            Console.Write("Hello");
            Console.Write(" ");
            Console.WriteLine("World");
            Console.WriteLine("Second line");
        }
    }
}

Hello World
Second line

Escape Characters

Certain characters inside strings must be escaped with a backslash \ to be represented correctly:

Example

using System;

namespace EscapeDemo
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("Line1\nLine2");
            Console.WriteLine("Name\tAge");
            Console.WriteLine("Path: C:\\Users\\Doc");
            Console.WriteLine("He said \"Hello\"");
        }
    }
}

Line1
Line2
Name	Age
Path: C:\Users\Doc
He said "Hello"

Warning: If a string contains many backslashes (such as file paths), use a verbatim string @"...", where \ no longer needs escaping.

Comments

Comments are notes for developers and are ignored by the compiler. C# supports three types of comments:

• //: Single-line comment; everything after // to the end of the line is ignored
• /* */: Multi-line comment; can span multiple lines
• ///: XML documentation comment; can generate API documentation

using System;

namespace CommentDemo
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("hello");

            Console.WriteLine("world");

            /*
            Console.WriteLine("skipped");
            Console.WriteLine("also skipped");
            */

            Console.WriteLine("end");
        }

        /// <summary>
        /// Calculate the sum of two numbers
        /// </summary>
        static int Add(int a, int b)
        {
            return a + b;
        }
    }
}

hello
world
end

Tip: XML documentation comments (///) are commonly used for public APIs. Visual Studio displays these descriptions when the method is called.

Top-Level Statements

Starting with C# 9, top-level statements let you skip the boilerplate namespace, class, and Main code, writing logic directly at the file's top level. The compiler automatically generates the entry method.

Example

using System;

Console.WriteLine("Top-level statement!");
int result = 40 + 2;
Console.WriteLine($"The answer is {result}");

Top-level statement!
The answer is 42

Tip: Top-level statements can only be used in one file per project. Using them in multiple files causes a compilation error.

File-Scoped Namespaces

Starting with C# 10, file-scoped namespaces let you use namespace MyApp; instead of the traditional block-style namespace, reducing one level of nesting:

namespace MyApp;

class Program
{
    static void Main()
    {
        Console.WriteLine("File-scoped namespace");
    }
}

This is equivalent to:

namespace MyApp
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("File-scoped namespace");
        }
    }
}

Tip: File-scoped namespaces make code more concise and are recommended for new projects.

❓ FAQ

📖 Summary

• A C# program consists of using directives, namespace, class, and Main method
• Every statement must end with a semicolon
• Code blocks are wrapped in braces and can be nested
• Console.Write does not add a newline; Console.WriteLine does
• Escape characters use a backslash prefix; verbatim strings @"..." avoid escaping
• Three comment types: single-line //, multi-line /* */, XML doc ///
• Top-level statements (C# 9+) simplify entry-point code
• File-scoped namespaces (C# 10+) reduce nesting levels

📝 Exercises

1. Write a console program that uses Console.Write and Console.WriteLine to output your name and age
2. Use escape characters to output three lines of text in a single Console.WriteLine statement
3. Rewrite a classic program structure using top-level statements
4. Add XML documentation comments to a method, including <summary> and <param> tags

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