File Comparer - C# Programming Exercise

// Import necessary namespaces for file handling
using System; // Basic input/output operations
using System.IO; // FileStream for reading files
using System.Text; // StringBuilder for efficient string handling

class FileComparer // Main class for the file comparison program
{
    static void Main(string[] args) // Entry point of the program
    {
        // Check if the correct number of arguments (input files) are provided
        if (args.Length != 2) // If not enough arguments are provided
        {
            Console.WriteLine("Usage: FileComparer  "); // Show usage instructions
            return; // Exit the program if the arguments are incorrect
        }

        string file1 = args[0]; // The first file name to compare
        string file2 = args[1]; // The second file name to compare

        // Check if both files exist
        if (!File.Exists(file1)) // If the first file does not exist
        {
            Console.WriteLine($"Error: The file {file1} does not exist."); // Inform the user about the missing file
            return; // Exit the program if the first file is missing
        }

        if (!File.Exists(file2)) // If the second file does not exist
        {
            Console.WriteLine($"Error: The file {file2} does not exist."); // Inform the user about the missing file
            return; // Exit the program if the second file is missing
        }

        try
        {
            // Open both files for reading using FileStream
            using (FileStream fs1 = new FileStream(file1, FileMode.Open, FileAccess.Read)) // Open the first file
            using (FileStream fs2 = new FileStream(file2, FileMode.Open, FileAccess.Read)) // Open the second file
            {
                // Compare file lengths first
                if (fs1.Length != fs2.Length) // If the file sizes are different
                {
                    Console.WriteLine("The files are different (different sizes)."); // Inform the user about different sizes
                    return; // Exit the program if the sizes don't match
                }

                // Use byte arrays to read the files in chunks
                byte[] buffer1 = new byte[1024]; // Buffer to hold data from the first file
                byte[] buffer2 = new byte[1024]; // Buffer to hold data from the second file

                int bytesRead1, bytesRead2; // Variables to store the number of bytes read from each file

                // Compare the files byte by byte
                while ((bytesRead1 = fs1.Read(buffer1, 0, buffer1.Length)) > 0) // Read from the first file
                {
                    bytesRead2 = fs2.Read(buffer2, 0, buffer2.Length); // Read from the second file

                    // If the number of bytes read is different, the files are different
                    if (bytesRead1 != bytesRead2)
                    {
                        Console.WriteLine("The files are different (different lengths in chunks)."); // Inform the user about the discrepancy
                        return; // Exit the program if the chunk sizes don't match
                    }

                    // Compare the bytes from both buffers
                    for (int i = 0; i < bytesRead1; i++) // Loop through the bytes read
                    {
                        if (buffer1[i] != buffer2[i]) // If a byte doesn't match
                        {
                            Console.WriteLine("The files are different (mismatch found)."); // Inform the user about the mismatch
                            return; // Exit the program if any byte doesn't match
                        }
                    }
                }

                // If all checks pass, the files are identical
                Console.WriteLine("The files are identical."); // Inform the user that the files are the same
            }
        }
        catch (Exception ex) // Catch any exceptions that occur during file reading or comparison
        {
            Console.WriteLine($"An error occurred: {ex.Message}"); // Display the error message
        }
    }
}