private void btnLogin_Click(object sender, EventArgs e)
        {
            if(ValidateUser(txtLoginID.Text,txtLoginPwd.Text ))
            {   
                DBHelper.Con.Open();
                string sql = string.Format("select count(*) from student where LoginId='{0}' and LoginPwd='{1}'",txtLoginID.Text,txtLoginPwd.Text);
                SqlCommand cmd = new SqlCommand(sql, DBHelper.Con);
                int i = (int)cmd.ExecuteScalar();
                if(i>0)
                    MessageBox.Show("登录成功");
                else
                    MessageBox.Show("登录失败");
                DBHelper.Con.Close();
            }
        }这是个连接了SQL的登录器。。- - 我们刚教到这里。  求这代码是啥意思if(ValidateUser(txtLoginID.Text,txtLoginPwd.Text ))