private void btn_View_Edit_inv_Click(object sender, EventArgs e)
 {
     try
     {
         int selected_Inv_ID        = Convert.ToInt16(dgv_search.CurrentRow.Cells[0].Value);
         frm_Sales_Invoice frm_edit = new frm_Sales_Invoice("Edit", selected_Inv_ID);
         frm_edit.ShowDialog();
     }
     catch (Exception exp)
     {
         MessageBox.Show(exp.Message);
     }
 }
        private void btn_New_Invoice_Click(object sender, EventArgs e)
        {
            frm_Sales_Invoice frm_sal_inv = new frm_Sales_Invoice("Add");

            frm_sal_inv.ShowDialog();
        }