How to stop threads in C#

using System;
using ;
using ;
using ;
using ;
using ;
using ;
using ;
namespace WinFormApp
{
 public partial class Form1 : Form
 {
   cancel = new ();
  [] thread;
  int len = 2;
  public Form1()
  {
   InitializeComponent();
   thread = new [len];
  }
  void RunThread()
  {
   (richTextBox1, "The thread is about to start running.");
    t = null;
   for (int i = 0; i < len; i++)
   {
    t = new (new (Sample));
     = "thread_0" + ();
     = true;
    (t, i);
    ();
   }
  }
  void Sample()
  {
   string name = ;
   (richTextBox1, "Running thread:" + name);
   while (true)
   {
    if ()
    {
     (richTextBox1, "Thread:" + name + "Stop running...");
     //Callback after thread is terminated     (delegate
     {
      (richTextBox1, "Thread:" + name + "Callback function after stopping...");
     });
     break;
    }
   }
  }
  void ShowStatu()
  {
   StringBuilder sb = new StringBuilder();
   for (int i = 0; i < len; i++)
   {
    if (thread[i].IsAlive == true)
    {
     ("Thread:" + thread[i].() + " Still running...");
    }
   }
   if (() == "")
   {
    ("The threads have all stopped...");
   }
    += ();
  }
  /// <summary>
  /// Start running the thread  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void button1_Click(object sender, EventArgs e)
  {
   RunThread();
  }
  /// <summary>
  /// Show all thread status  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void button2_Click(object sender, EventArgs e)
  {
   ShowStatu();
  }
  /// <summary>
  /// Terminate all threads  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void button3_Click(object sender, EventArgs e)
  {
   ();
  }
 }
}