C#

public partial class Form1 : Form
{
    Form2 form2;

    public Form1()
    {
        InitializeComponent();
        form2 = new Form2(this.Handle);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        this.Hide();
        form2.Show();
    }
}

public partial class Form2 : Form
{
    private IntPtr friendHandle;

    public Form2(IntPtr hnd)
    {
        InitializeComponent();

        friendHandle = hnd;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        this.Hide();
        Form.FromHandle(friendHandle).Show();
    }
}

holdLine = Regex.Replace("\r(?!\n)")

string result = "";<br />
foreach(object item in ArrayList)<br />
{<br />
   result += item.ToString() + " ";<br />
}<br />
result = result.TrimEnd(new string[]{" "});

StringBuilder result = new StringBuilder();
foreach(object item in ArrayList)
{
  result.AppendLine(item.ToString());
}
String result2 = result.ToString();

StringBuilder result = new StringBuilder();
foreach(object item in ArrayList)
{
  result.Append(item.ToString() + " ");
}
String result2 = result.ToString();
result2 = result2.Remove(result2.Length-1);

Deresen wrote:

result.Append(item.ToString() + " ");

result.Append(item.ToString());
result.Append(" ");

ArrayList temp = new ArrayList();
temp.Add("A");
temp.Add("B");

string delim = " "; //space
string result = string.Join(delim, (string[])temp.ToArray(typeof(string)));

//result will be "A B"