SwtichCaseWithRangeVersion2.cs

public string ConvertFileSize(long size)
{
    switch (size)
    {
        case var _ when size < 1024:
            return $"{size} Bytes";
        case var _ when size >= 1024 && size < Math.Pow(1024, 2):
            return $"{size / 1024:N2} KB";
        case var _ when size >= Math.Pow(1024, 2) && size < Math.Pow(1024, 3):
            return $"{size / Math.Pow(1024, 2):N2} MB";
        case var _ when size >= Math.Pow(1024, 3):
            return $"{size / Math.Pow(1024, 3):N2} GB";
        default:
            return size.ToString();
    }
}