ERROR- inavalid token BOOL in class

Question

i wrote a program of thread as  below and it is showing error as INAVALID TOKEN BOOL IN CLASS,INTERFACE OR METHOD

using System;

using System.Threading;

namespace ConsoleApplication1

{

public class worker

{

public void dowork()

{

while (!_shouldstop)

{

Console.WriteLine("doworker thread is proessing ");

}

Console.WriteLine("doworker thread is terminating ");

}

public void requeststop()

{

_shouldstop=true;

}

private Volatile bool _shouldstop;

}

public class workerthreadex

{

static void Main()

{

worker ws = new worker();

Thread th = new Thread(ws.dowork);

th.Start();

Console.WriteLine("main function starting do work thread");

while(th.IsAlive)

{

Thread.Sleep(1);

}

ws.requeststop();

th.Join();

Console.WriteLine("thread terminated successfully");

Console.ReadKey();

}

}

}