SwitchCaseWithRange.cs

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