private void BtnIngresar_Click(object sender, EventArgs e)
        {
            bool             blnfound = false;
            NpgsqlConnection conn     = new NpgsqlConnection("Server=localhost; Port=5432; User Id=postgres; Password=1234; Database=Login");

            conn.Open();
            NpgsqlCommand    cmd = new NpgsqlCommand("select * from usuarios where cedula='" + TxtCi.Text + "' and contra='" + TxtContra.Text + "'", conn);
            NpgsqlDataReader dr  = cmd.ExecuteReader();

            if (dr.Read())
            {
                blnfound = true;
                this.Hide();
                FrmFormularios fr = new FrmFormularios();
                fr.FormClosed += (s, args) => this.Close();
                fr.Show();
            }
            if (blnfound == false)
            {
                MessageBox.Show("EL NOMBRE O LA CONTRASEÑA SON INCORRECTOS", "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
            }

            dr.Close();
            conn.Close();
        }
        private void BtnAtras_Click(object sender, EventArgs e)
        {
            this.Hide();
            FrmFormularios fr = new FrmFormularios();

            fr.FormClosed += (s, args) => this.Close();
            fr.Show();
        }