if (dataGridView2.SelectedRows.Count == 0)
{
textBox19.Text = (Convert.ToInt32(textBox19.Text) - Convert.ToInt32(dataGridView2.Rows[dataGridView2.SelectedCells[0].RowIndex].Cells[3].Value)).ToString();
}
else
{
textBox19.Text = (Convert.ToInt32(textBox19.Text) - Convert.ToInt32(dataGridView2.SelectedRows[0].Cells[3].Value)).ToString();
}