C#

string mac1 = "00204A846187";
string mac2 = mac1.Insert(10, "-").Insert(8, "-").Insert(6, "-").Insert(4, "-").Insert(2, "-");
Console.WriteLine(mac1 + " converted to: " + mac2);

mac2 = string.Format("{0:x2}-{1:x2}-{2:x2}-{3:x2}-{4:x2}-{5:x2}", 
                     mac1.Substring(0,2), 
                     mac1.Substring(2,2),
                     mac1.Substring(4,2),
                     mac1.Substring(6,2),
                     mac1.Substring(8,2),
                     mac1.Substring(10,2));

StringBuilder mac2 = new StringBuilder();
mac2.AppendFormat("{0:x2}", mac1.Substring(0,2));
mac2.AppendFormat("{0:x2}", mac1.Substring(2,2));
mac2.AppendFormat("{0:x2}", mac1.Substring(4,2));
mac2.AppendFormat("{0:x2}", mac1.Substring(6,2));
mac2.AppendFormat("{0:x2}", mac1.Substring(8,2));
mac2.AppendFormat("{0:x2}", mac1.Substring(10,2));

string mac2 = "";
for (int i = 0; i < mac1.Length; i++)
{
    mac2 += mac1[i];
    if ((i + 1) % 2 == 0 && i < mac1.Length-1)
    {
        mac2 += "-";
    }
}

public class MACAddress
{
    const string separator = "-";
    public int[] Octets = new int[6];
    public string Mac 
    {
        get 
        { 
            StringBuilder str = new StringBuilder();
            for(int i = 0; i < Octets.Length; i++)
            {
                str.AppendFormat("{0:x2}", Octets[i]);
                if (i < Octets.Length - 1)
                {
                    str.Append(separator);
                }
            }
    }

    public MACAddress(string address)
    {
        if (ValidateAddress(ref address))
        {
            Parse(address)
        }
    }

    private bool Validate(ref string address)
    {
        address = address.Replace("-", "").Replace(":", "").Replace(" ", "").ToUpper().Trim();
        if (address.Length != 12)
        {
            throw new Exception("Invalid mac address specified. Must be exactly 12 valid alphanumeric characters");
        }
        string validCharacters = "0123456789ABCDEF";
        var count = (from c in address 
                     where !validCharacters.Contains(c)
                     select c).Count;
        if (count > 0)
        {
            throw new Exception("Invalid MAC address specified. One or more invalid characters detected.");
        }
    }

    private void Parse(string address)
    {
        for (int i = 10; i > 0; i-2)
        {
            address = address.Insert(i,":");
        }
        string[] parts = address.Split(":");
        for (int i = 0; i < parts.Length; i++)
        {
            Int32.TryParse(parts[i], out Octets[i]);
        }
    }
}

clsUsage _clsUsage = new clsUsage();<br />
_clsUsage.CalcUsage();<br />

frmStatus _frmStatus = new frmStatus();<br />
_frmStatus.Show();<br />
//doing some operations and modifying attributes to controls of frmStatus form<br />
_frmStatus.Close();

//created a property in action class<br />
private Form parentForm;<br />
<br />
public Form ParentForm<br />
{<br />
   get { return parentForm; }<br />
   set { parentForm = value; }<br />
}<br />
<br />
//in frmMain in clicked event added<br />
_clsUsage.ParentForm = this;<br />
<br />
//in the action class in the action method<br />
_frmStatus.Parent = ParentForm;

private void dgcboDocNo_SelectedIndexChanged(object sender, EventArgs e)
{
    System.Diagnostics.Debug.WriteLine(dataGridView1.CurrentCell.ColumnIndex + "SelectedIndexChanged");

    string docno = ((DataGridViewComboBoxEditingControl)sender).Text.ToString();
    DataRow[] dr = myDs.Tables["DetailDocRegister"].Select("DocNo = '" + docno + "'");
    if (dr.Length > 0)  // <======================= TEST HERE ======================================================
    {
        int y = dataGridView1.CurrentCellAddress.Y;
        dataGridView1.Rows[y].Cells[1].Value = dr[0]["DocTitle"];
    }
}

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    DataGridViewComboBoxEditingControl combo = e.Control as DataGridViewComboBoxEditingControl;  // <=============== HERE ================
    System.Diagnostics.Debug.WriteLine(dataGridView1.CurrentCell.ColumnIndex + "EditControlShowing");
    if (combo != null)
    {
        combo.SelectedIndexChanged -= new EventHandler(dgcboDocNo_SelectedIndexChanged);
        combo.SelectedIndexChanged += new EventHandler(dgcboDocNo_SelectedIndexChanged);
    }
}

public static void CopyDirectory(string source, string destination, bool overwrite)
       {
           // Create the destination folder if missing.
           if (!Directory.Exists(destination))
               Directory.CreateDirectory(destination);

           DirectoryInfo dirInfo = new DirectoryInfo(source);

           // Copy all files.
           foreach (FileInfo fileInfo in dirInfo.GetFiles())
               fileInfo.CopyTo(Path.Combine(destination, fileInfo.Name), overwrite);

           // Recursively copy all sub-directories.
           foreach (DirectoryInfo subDirectoryInfo in dirInfo.GetDirectories())
               CopyDirectory(subDirectoryInfo.FullName, Path.Combine(destination, subDirectoryInfo.Name), overwrite);
       }