private void button3_Click_1(object sender, EventArgs e)
        {
            注册界面 mylogin = new 注册界面();
            mylogin.Show();
        }

private void skinButton1_Click_3(object sender, EventArgs e)
        {
            System.Diagnostics.Process.Start("osk.exe");
        }

 

 bool random0 =true;//验证码判断标志
//更换验证码
private void txtpwd_TextChanged(object sender, EventArgs e)
        {
            if (random0)
            {
            Random random = new Random();
            int minV = 1234, maxV = 9876;
            checkcode.Text = random.Next(minV, maxV).ToString();
            random0 = !random0;
            }
            
        }