Question

when I click button1 should print A s but when I click button2 need to stop thread1 and need to start thread2, what is the wrong in here please help me

    private void button1_Click(object sender, EventArgs e)
    {
        if (thread2.IsAlive)
        {
            thread2.Suspend();
        }
        thread1 = new Thread(threadOne);
        thread1.Start();
    }

    private void button2_Click(object sender, EventArgs e)
    {
        if (thread1.IsAlive)
        {
            thread1.Suspend();
        }
        thread2 = new Thread(threadTwo);
        thread2.Start();
    }

    private void threadOne() {
        for (int i=0; i < 20; i++ )
        {
            Console.Write("A");
            Thread.Sleep(500);
        }
    }

    private void threadTwo()
    {
        for (int i = 0; i < 20; i++)
        {
            Console.Write("B");
            Thread.Sleep(500);
        }
    }

Answer 1

There’s quite a lot wrong, as the other posters have correctly pointed out. I would add this:

1) Most threads in commercial-grade software never terminate during the lifetime of the application – they are written as infinite loops with blocking calls that wait for some sort of signaling from other threads or I/O operations.

2) Continual create/terminate/destroy of thread objects is expensive, difficult to control, awkward-to-debug, unreliable and generally causes pain.

3) If your multithread code contains any of the following:

Suspend()
Resume(), (except in some thread ctors)
Join()
Abort()
IsAlive()

You should probably think again 🙂

I know you’re only learning, but sometimes it’s better to patch up holes before they get any bigger 🙂