private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                //var sr = new System.IO.StreamReader("C:\\" + textBox1.Text + "\\login.ID");
                //username = sr.ReadLine();
                //password = sr.ReadLine();
                //sr.Close();

                if (username == textBox1.Text && password == textBox2.Text)
                {
                    MessageBox.Show("you are now successfully logged in!", "Success");
                    BookCatalogue buchcatalog = new BookCatalogue();
                    buchcatalog.Show();
                }
                else
                {
                    MessageBox.Show("Username or Password is wrong!", "Error!");
                }
            }
            catch (System.IO.DirectoryNotFoundException ex)
            {
                MessageBox.Show("The user does not exit!", "Error!");
            }
        }
        private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                //var sr = new System.IO.StreamReader("C:\\" + textBox1.Text + "\\login.ID");
                //username = sr.ReadLine();
                //password = sr.ReadLine();
                //sr.Close();

                if (username == textBox1.Text && password == textBox2.Text)
                {
                    MessageBox.Show("you are now successfully logged in!", "Success");
                    BookCatalogue buchcatalog = new BookCatalogue();
                    buchcatalog.Show();
                }
                else
                    MessageBox.Show("Username or Password is wrong!", "Error!");
            }
            catch (System.IO.DirectoryNotFoundException ex)
            {
               MessageBox.Show("The user does not exit!", "Error!");
            }
        }