C#

<br />
using System;<br />
using System.Collections.Generic;<br />
using System.Text;<br />
using System.IO;<br />
<br />
namespace drives<br />
{<br />
    class Program<br />
    {<br />
        static void Main(string[] args)<br />
        {<br />
            // build a List<int> representing the ASCII values of all drives<br />
            int intFirstDrive = Convert.ToInt32('A');<br />
            int intLastDrive = Convert.ToInt32('Z');<br />
            List<int> intAvailableDrives = new List<int>();<br />
            for (int i = intFirstDrive; i <= intLastDrive; i++)<br />
            {<br />
                intAvailableDrives.Add(i);<br />
            }<br />
<br />
            // get all current drives<br />
            DriveInfo[] usedDrives = DriveInfo.GetDrives();<br />
            int x = usedDrives.Length;<br />
<br />
            // remove used drives<br />
            foreach (DriveInfo usedDrive in usedDrives)<br />
            {<br />
                int intUsedDrive;<br />
                string strUsedDrive;<br />
                char chrUsedDrive;<br />
                strUsedDrive = usedDrive.Name.Substring(0, 1);<br />
                chrUsedDrive = Convert.ToChar(strUsedDrive);<br />
                intUsedDrive = Convert.ToInt32(chrUsedDrive);<br />
                intAvailableDrives.Remove(intUsedDrive);<br />
            }<br />
<br />
            // convert the ASCII values of the available drives to string<br />
            List<string> strAvailableDrives = intAvailableDrives.ConvertAll<string>(delegate<br />
                (int intDrive)<br />
                {<br />
                    return Convert.ToChar(intDrive).ToString();<br />
                });<br />
        }<br />
    }<br />
}<br />