private void button1_Click(object sender, EventArgs e)
        {
            kullaniciSayfasi kullaniciSayfasi = new kullaniciSayfasi();

            this.Hide();
            kullaniciSayfasi.Show();
        }
        private void btn_login_Click(object sender, EventArgs e)
        {
            eposta = txt_username.Text;
            sifre  = txt_password.Text;
            SqlConnection  sqlcon = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\DKE10017\source\repos\ShiftManagementSystem\ShiftManagementSystem\db\DB.mdf;Integrated Security=True;Connect Timeout=30");
            string         query  = "Select * from tbl_Login where eposta ='" + eposta.Trim() + "' and password = '******'";
            SqlDataAdapter sda    = new SqlDataAdapter(query, sqlcon);
            DataTable      dtbl   = new DataTable();

            sda.Fill(dtbl);
            if (dtbl.Rows.Count >= 1)
            {
                kullaniciSayfasi kullaniciSayfasi = new kullaniciSayfasi();
                this.Hide();
                kullaniciSayfasi.Show();
            }
            else
            {
                MessageBox.Show("Kullanıcı adınız veya şifreniz hatalıdır.");
            }
        }