Writing and Running Your First C# Program

Introduction

In this chapter, we will learn how to create and run your first C# program: Hello World. This simple program will introduce you to the basic structure of a C# application and how to compile and run it using different development environments.

Creating Your First C# Project

Using the .NET CLI

The .NET Command Line Interface (CLI) is used for creating, building, and running .NET applications. Follow these steps to create and run your first C# program using the .NET CLI:

Open a Command Prompt or Terminal.
Create a New Project: Run the following command to create a new console application:
```
dotnet new console -n MyFirstApp
```
This command creates a new directory called MyFirstApp with a basic C# console application.
Navigate to the Project Directory:
```
cd MyFirstApp
```
Run the Project:
```
dotnet run
```
This command compiles and runs the application, displaying "Hello World!" in the console.

Using Visual Studio

Visual Studio is a powerful Integrated Development Environment (IDE) for C# development. Follow these steps to create and run your first C# program using Visual Studio:

Open Visual Studio.
Create a New Project:
- Click on "Create a new project".
- Select "Console App (.NET Core)" and click "Next".
- Name your project "MyFirstApp" and choose a location to save it.
- Click "Create".

Write Your Code:

Visual Studio automatically generates a basic console application. Open the Program.cs file, which contains the following code:

using System;

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

Run the Project:
- Click the green "Start" button or press F5 to build and run the application. The output window will display "Hello, World!".

Using Visual Studio Code

Visual Studio Code is a lightweight, cross-platform code editor that supports C# development through extensions. Follow these steps to create and run your first C# program using Visual Studio Code:

Open Visual Studio Code.
Open the Terminal: Go to View > Terminal or press Ctrl+` to open the integrated terminal.
Create a New Project:
- In the terminal, run:
```
dotnet new console -n MyFirstApp
```
Open the Project:
- Open the project folder in Visual Studio Code by going to File > Open Folder and selecting the MyFirstApp directory.

Write Your Code:

Open the Program.cs file, which contains the following code:

using System;

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

Run the Project:
- In the terminal, run:
```
dotnet run
```
This command compiles and runs the application, displaying "Hello, World!" in the terminal.

Understanding the Code

Here’s a breakdown of the basic C# program:

using System;

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

using System;: This statement includes the System namespace, which contains fundamental classes for input and output operations.
namespace MyFirstApp: A namespace is used to organize code and prevent naming conflicts.
class Program: A class is a blueprint for creating objects. The Program class contains the code for our application.
static void Main(string[] args): The Main method is the entry point of the application. It is where the program starts executing.
Console.WriteLine("Hello, World!");: This line prints the string "Hello, World!" to the console.

Conclusion

Congratulations! You have successfully written and run your first C# program. This simple "Hello, World!" application introduces you to the basic structure of a C# program and how to use different development environments to create and run C# applications. In the next chapters, we will dive deeper into the fundamentals of C# programming, including variables, data types, control flow, and more.