Reading A Binay File (2 - GIF) - C# Programming Exercise

// Importing necessary namespaces
using System; // Importing the System namespace for basic C# functionality
using System.IO; // Importing the IO namespace for file operations

public class GifFileChecker
{
    // Method to check if the GIF file seems to be correct and to display the GIF version
    public static void CheckGifFile(string fileName)
    {
        // Open the file in binary mode for reading
        using (BinaryReader reader = new BinaryReader(File.Open(fileName, FileMode.Open))) // Use BinaryReader to read bytes from the file
        {
            // Read the first four bytes of the file to check the header
            byte[] header = reader.ReadBytes(4); // Read the first 4 bytes

            // Check if the first four bytes are G, I, F, and 8
            if (header[0] == 0x47 && header[1] == 0x49 && header[2] == 0x46 && header[3] == 0x38) // Check if the bytes match "GIF8"
            {
                // Display that the file is a valid GIF file
                Console.WriteLine("This is a valid GIF file.");

                // Read the next byte to determine the GIF version
                byte versionByte = reader.ReadByte(); // Read the next byte

                // Check the version byte for 87 or 89
                if (versionByte == 0x37) // If the byte is 0x37 (ASCII for "7"), it is GIF 87
                {
                    Console.WriteLine("GIF Version: 87a"); // Display the GIF version
                }
                else if (versionByte == 0x39) // If the byte is 0x39 (ASCII for "9"), it is GIF 89
                {
                    Console.WriteLine("GIF Version: 89a"); // Display the GIF version
                }
                else
                {
                    Console.WriteLine("Unknown GIF version.");
                }
            }
            else
            {
                // If the first four bytes don't match "GIF8", it's not a valid GIF file
                Console.WriteLine("This is not a valid GIF file.");
            }
        }
    }
}

class Program
{
    // Main method where the program execution starts
    static void Main(string[] args)
    {
        // Check if the user provided the file name as an argument
        if (args.Length < 1) // If no file name is provided
        {
            Console.WriteLine("Please provide the GIF file name."); // Prompt user to provide the file
            return; // Exit the program if no file is provided
        }

        string fileName = args[0]; // Assign the file name from the command line argument

        // Check if the input file exists
        if (!File.Exists(fileName)) // If the file doesn't exist
        {
            Console.WriteLine($"The file '{fileName}' does not exist."); // Print error message
            return; // Exit the program if the file doesn't exist
        }

        // Call the method to check the GIF file
        GifFileChecker.CheckGifFile(fileName); // Check the file and display the result
    }
}