C#

There are three built-in service accounts:

. LocalSystem: The LocalSystem account is a predefined local account.
It has extensive privileges on the local computer, and acts as the computer
on the network. The name of the account is LocalSystem. This account does
not have a password.

. LocalService: The LocalService account is a predefined local
account. It has minimum privileges on the local computer and presents
anonymous credentials on the network. The name of the account is NT
AUTHORITY\LocalService. This account does not have a password.

. NetworkService: The NetworkService account is a predefined local
account. It has minimum privileges on the local computer and acts as the
computer on the network. The name of the account is NT
AUTHORITY\NetworkService. This account does not have a password.

using System;
using System.Drawing;
using System.Windows.Forms;
 
class ParentForm : Form // Default access for class is internal
{
  static void Main()
  {
    Application.Run(new ParentForm());
  }
 
  Button openChild; // Default access is private for class members
  internal TextBox childText; // Make accessible to child form in this assembly
  internal ParentForm()
  {
    Text = "Example: Parent Form";
 
    openChild = new Button();
    Controls.Add(openChild);
    openChild.Location = new Point(8, 8);
    openChild.Text = "Open Child";
    openChild.Click += new EventHandler(openChild_Click);
 
    childText = new TextBox();
    Controls.Add(childText);
    childText.Location = new Point(8, openChild.Bottom + 8);
    childText.ReadOnly = true;
  }
 
  void openChild_Click(object sender, EventArgs e)
  {
    using (ChildForm form = new ChildForm())
      form.ShowDialog(this);
  }
}
 
class ChildForm : Form
{
  TextBox myText;
  internal ChildForm()
  {
    Text = "Example: Child Form";
 
    myText = new TextBox();
    Controls.Add(myText);
    myText.Location = new Point(8, 8);
    myText.TextChanged += new EventHandler(myText_TextChanged);
  }
 
  void myText_TextChanged(object sender, EventArgs e)
  {
    ParentForm parent = Owner as ParentForm;
    if (parent != null)
      parent.childText.Text = myText.Text;
  }
}