C# string.format with decimal format.

Question

DriveInfo[] drives = DriveInfo.GetDrives();
for (int i = 0; i < drives.Length; i++)
{
    if (drives[i].IsReady)
    {
        Console.WriteLine("Drive {0} - Has free space of {1} GB",drives[i].ToString(),(drives[i].TotalFreeSpace/1024/1024/1024).ToString("N2"));
    }
}

Output:

Drive C:\ - Has free space of 70,00 GB
Drive D:\ - Has free space of 31,00 GB
Drive E:\ - Has free space of 7,00 GB
Drive F:\ - Has free space of 137,00 GB

All end up with ,00 but I need to show real size. So which format is suitable?

Answer 1

The format string doesn't have anything to do with it. Your integer operations are discarding any remainder.

3920139012 / 1024 / 1024  / 1024 // 3

Specify decimals using the m suffix like so:

3920139012 / 1024m / 1024m / 1024m // 3.6509139575064182281494140625

Alternatively:

3920139012 / Math.Pow(1024, 3) // 3.65091395750642

This might be a little more clear:

var gb = Math.Pow(1024, 3);
foreach(var drive in DriveInfo.GetDrives())
{   
    if(drive.IsReady)
    {
        Console.WriteLine("Drive {0} - Has free space of {1:n2} GB",
            drive.Name,
            drive.TotalFreeSpace / gb);
    }
}

Answer 2

Becasue you are doing integer division which truncates decimal remainders. Use floating-point division instead:

drives[i].TotalFreeSpace/1024.0/1024.0/1024.0

or

drives[i].TotalFreeSpace / (1024.0 * 1024.0 * 1024.0)