📚 Reading and Writing Files in C# 📚

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🥔 What is File Handling?

In C#, file handling lets you work with files stored on your computer. You can:

✅ Read files – Get data from a file.
✅ Write to files – Save data to a file.
✅ Append data – Add more information without deleting what’s already there.

Imagine a magic notebook 📔 where you can read what’s written inside, write new things, or add more notes later without erasing anything! ✏️✨

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🎯 Why Do We Need File Handling?

1. Save Information Permanently – Unlike variables that are lost when the program ends, data stored in files stays there.
2. Load and Process Large Data – Read large amounts of information from a file and process it.
3. Store User Preferences – Save user settings that can be reloaded the next time the app runs.
4. Data Exchange – Share information between different applications.

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📄 Basic Concepts of File Handling

There are three main classes in the System.IO namespace that help you handle files:

1. File – Provides methods to perform file operations.
2. StreamReader – Reads data from a file.
3. StreamWriter – Writes data to a file.

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🎁 Let’s Explore with a Story!

🥔 Meet PotatoScript! PotatoScript wants to write a list of ingredients for her favorite potato recipes and read them later. 🍟

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📝 Step 1: Writing to a File

To write data to a file, use the StreamWriter class.

📄 Basic Structure for Writing:

using System;
using System.IO;

class Program
{
    static void Main()
    {
        // Create a file and write data to it
        using (StreamWriter writer = new StreamWriter("potato_recipes.txt"))
        {
            writer.WriteLine("🥔 Potato Fries");
            writer.WriteLine("🥔 Mashed Potatoes");
            writer.WriteLine("🥔 Potato Salad");
            Console.WriteLine("Recipes have been written to the file! 📄");
        }
    }
}

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🧠 Explanation:

• StreamWriter – Writes data to the file potato_recipes.txt.
• writer.WriteLine() – Writes one line at a time.
• using – Ensures the file is closed properly after writing.

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🎁 Output:

Recipes have been written to the file! 📄

A file named potato_recipes.txt is created with the following content:

🥔 Potato Fries
🥔 Mashed Potatoes
🥔 Potato Salad

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📝 Step 2: Reading from a File

To read data from a file, use the StreamReader class.

📄 Basic Structure for Reading:

using System;
using System.IO;

class Program
{
    static void Main()
    {
        // Read data from the file
        using (StreamReader reader = new StreamReader("potato_recipes.txt"))
        {
            string recipe;
            while ((recipe = reader.ReadLine()) != null)
            {
                Console.WriteLine("🍴 " + recipe);
            }
        }
    }
}

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🧠 Explanation:

• StreamReader – Reads data from the file potato_recipes.txt.
• reader.ReadLine() – Reads one line at a time.
• The while loop continues until there are no more lines to read.

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🎁 Output:

🍴 🥔 Potato Fries
🍴 🥔 Mashed Potatoes
🍴 🥔 Potato Salad

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✨ Step 3: Appending Data to a File

To add more data without deleting what’s already there, use StreamWriter with the append parameter set to true.

📄 Basic Structure for Appending:

using System;
using System.IO;

class Program
{
    static void Main()
    {
        // Append data to the file
        using (StreamWriter writer = new StreamWriter("potato_recipes.txt", true))
        {
            writer.WriteLine("🥔 Baked Potatoes");
            writer.WriteLine("🥔 Potato Soup");
            Console.WriteLine("More recipes have been added! 🍲");
        }
    }
}

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🧠 Explanation:

• StreamWriter("potato_recipes.txt", true) – Opens the file in append mode.
• true ensures new data is added at the end.

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🎁 Output:

More recipes have been added! 🍲

The file now contains:

🥔 Potato Fries
🥔 Mashed Potatoes
🥔 Potato Salad
🥔 Baked Potatoes
🥔 Potato Soup

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📂 Working with File Class for Simpler Operations

The File class in System.IO provides easier ways to perform file operations like reading and writing.

📄 Writing with File.WriteAllText()

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string content = "🥔 Potato Fries\n🥔 Mashed Potatoes\n🥔 Potato Salad";
        
        // Write to the file
        File.WriteAllText("potato_recipes.txt", content);
        Console.WriteLine("Recipes written using File.WriteAllText()!");
    }
}

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📄 Reading with File.ReadAllText()

using System;
using System.IO;

class Program
{
    static void Main()
    {
        // Read all content from the file
        string content = File.ReadAllText("potato_recipes.txt");
        Console.WriteLine("Here are the recipes:\n" + content);
    }
}

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📄 Appending with File.AppendAllText()

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string moreContent = "\n🥔 Baked Potatoes\n🥔 Potato Soup";
        
        // Append data
        File.AppendAllText("potato_recipes.txt", moreContent);
        Console.WriteLine("More recipes added using File.AppendAllText()!");
    }
}

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⚡ Reading and Writing with FileStream

For advanced file operations, use FileStream to read and write binary data.

📄 Example of Writing Binary Data:

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string data = "PotatoScript loves coding! 🥔💻";
        byte[] bytes = System.Text.Encoding.UTF8.GetBytes(data);

        using (FileStream fs = new FileStream("potato_data.bin", FileMode.Create))
        {
            fs.Write(bytes, 0, bytes.Length);
            Console.WriteLine("Binary data written to file!");
        }
    }
}

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📄 Example of Reading Binary Data:

using System;
using System.IO;

class Program
{
    static void Main()
    {
        using (FileStream fs = new FileStream("potato_data.bin", FileMode.Open))
        {
            byte[] bytes = new byte[fs.Length];
            fs.Read(bytes, 0, bytes.Length);
            string data = System.Text.Encoding.UTF8.GetString(bytes);
            Console.WriteLine("Data read from file: " + data);
        }
    }
}