private void insertbtn_Click(object sender, EventArgs e) { if (titletb.Text != "" && categorycb.Text != "" && authorcb.Text != "" && qtytb.Text != "" && pricetb.Text != "") { if (lc.verifyCategory(dt1, categorycb.Text) && lc.verifyAuthor(dt2, authorcb.Text)) { MessageBox.Show(lc.addBook(titletb.Text, categorycb.SelectedValue.ToString(), authorcb.SelectedValue.ToString(), int.Parse(pricetb.Text), int.Parse(qtytb.Text))); } else if (!lc.verifyCategory(dt1, categorycb.Text) && lc.verifyAuthor(dt2, authorcb.Text)) { int catid = lc.addBookcategory(categorycb.Text); MessageBox.Show(lc.addBook(titletb.Text, catid.ToString(), authorcb.SelectedValue.ToString(), int.Parse(pricetb.Text), int.Parse(qtytb.Text))); } else if (lc.verifyCategory(dt1, categorycb.Text) && !lc.verifyAuthor(dt2, authorcb.Text)) { int authid = lc.addBookauthor(authorcb.Text); MessageBox.Show(lc.addBook(titletb.Text, categorycb.SelectedValue.ToString(), authid.ToString(), int.Parse(pricetb.Text), int.Parse(qtytb.Text))); } else if (!lc.verifyCategory(dt1, categorycb.Text) && !lc.verifyAuthor(dt2, authorcb.Text)) { int catid = lc.addBookcategory(categorycb.Text); int authid = lc.addBookauthor(authorcb.Text); MessageBox.Show(lc.addBook(titletb.Text, catid.ToString(), authid.ToString(), int.Parse(pricetb.Text), int.Parse(qtytb.Text))); } } else { MessageBox.Show("Please enter all details", "Error"); } }