public enum RunState
{
     running,
     pause,
     suppend
}

RunState state = RunState.suppend;
bool Restart = false;

RunProc(...)//执行的部分
{
     while(state != RunState.suppend)
     {
          //执行操作
           Application.DoEvents();
          if(state == RunState.suppend) break;//保证可以正常退出
          while(state == RunState.pause)//保证可以暂停，不过这样效率不高：）但实现这个功能也只能如此了。
          {
               Application.DoEvents();
          }
     }
     if(Restart)
     {
          Restart = False;
          Button2.PerformClick();
     }
}

Button2_Clicked(...)//开始
{
     if(state != RunState.suppend)
     {
          state = RunState.suppend;
          Restart = true;
     }
     state = RunState.running;
     RunProc();
}

Button3_Clicked(...)//暂停
{
     state = RunState.pause;
}

Button4_Clicked(...)//停止
{
     state = RunState.suppend;
}

------解决方案--------------------
没有编译器调试，就随手写的，貌似上面写错了一点。用下面的
C# code


public enum RunState
{
     running,
     pause,
     suppend
}

RunState state = RunState.suppend;
bool Restart = false;

RunProc(...)//执行的部分
{
     while(state != RunState.suppend)
     {
          //....................//
          //执行你的操作
          Application.DoEvents();
          if(state == RunState.suppend) break;//保证可以正常退出
          while(state == RunState.pause)//保证可以暂停，不过这样效率不高：）但实现这个功能也只能如此了。
          {
               Application.DoEvents();
          }
     }
     if(Restart)
     {
          Restart = False;
          Button2.PerformClick();
     }
}

Button2_Clicked(...)//开始
{
     if(state != RunState.suppend)
     {
          state = RunState.suppend;
          Restart = true;
          return;//修改了这里，要退出栈
     }
     state = RunState.running;
     RunProc();
}

Button3_Clicked(...)//暂停
{
     state = RunState.pause;
}

Button4_Clicked(...)//停止
{
     state = RunState.suppend;
}

------解决方案--------------------
改了下，Restart没看出有什么实际的用处所以删掉了。
这个最好还是用线程或者BackgroundWorker，用法很简单，参考MSDN
       public enum RunState
       {
           running,
           pause,
           suppend
       }

       RunState state = RunState.suppend;
       int i = 0;

       private void RunProc()//执行的部分
       {
           while(i<10000)
           {
               label1.Text = i.ToString();
               label1.Refresh();
               System.Threading.Thread.Sleep(200);
               Application.DoEvents();
               if (state == RunState.suppend)
               {
                   i = 0;
                   label1.Text = i.ToString();
                   label1.Refresh();
                   break;//保证可以正常退出
               }
               while (state == RunState.pause)//保证可以暂停，不过这样效率不高：）但实现这个功能也只能如此了。
               {
                   Application.DoEvents();
               }

               i++;
           }
       }

       private void button1_Click(object sender, EventArgs e)
       {