C# Syntax and First Program

# CHAPTER 3

C# Syntax and First Program #

1. Introduction #

2. Learning Objectives #

• Understand the basic structure of a C# program.

• Explain the role of using, namespace, class, and Main().

• Print text to the screen using Console.WriteLine().

• Add single-line and multi-line comments to your code.

3. Dissecting "Hello World" #

using System;

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

Let's break it down line by line:

*(Note: Starting in C# 9 / .NET 6, Microsoft introduced Top-Level Statements. You can now literally just write Console.WriteLine("Hello, World!"); in a new file, and the compiler will generate the namespace, class, and Main method for you behind the scenes. However, understanding the classic structure is essential for enterprise development).*

4. Printing Output #

• Console.WriteLine(): Prints text and adds a newline at the end.

• Console.Write(): Prints text but keeps the cursor on the same line.

Console.Write("Hello ");
Console.Write("World!");
// Output: Hello World!

5. Comments in C# #

// This is a single-line comment. Useful for quick notes.

/* 
   This is a multi-line comment.
   It can span across several lines.
   Useful for temporarily disabling chunks of code.
*/

6. Mini Project: Simple Output Formatting #

using System;

namespace ReceiptPrinter
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("========================");
            Console.WriteLine("      STARBUCKS         ");
            Console.WriteLine("========================");
            Console.WriteLine("1x Coffee      $3.50");
            Console.WriteLine("1x Muffin      $2.00");
            Console.WriteLine("------------------------");
            Console.WriteLine("TOTAL:         $5.50");
            Console.WriteLine("========================");
        }
    }
}

7. OOP and Memory Explanations #

8. Common Mistakes #

• Forgetting the Semicolon: Every statement in C# must end with a ;. Missing this is the most common beginner error.

• Case Sensitivity: console.writeline() will fail. It must be capitalized exactly as Console.WriteLine().

• Mismatched Braces: Every opening brace { must have a corresponding closing brace }.

9. Best Practices #

• Always indent code inside curly braces. Visual Studio does this automatically, but keeping code clean is vital for readability.

• Use comments to explain *why* you did something, not *what* you did.

10. Exercises #

1. 1. Write a C# program that prints a triangle made of asterisks (*) to the console using multiple Console.WriteLine() statements.

1. 2. Intentionally remove a semicolon from your program and try to run it. Observe the error message in Visual Studio.

11. MCQs with Answers #

12. Interview Questions #

• Q: Explain the purpose of the static keyword in static void Main().

• Q: What is the difference between Console.Write and Console.WriteLine?

• Q: Why do we use namespaces in enterprise C# applications?

13. Summary #

14. Next Chapter Recommendation #