//声明字符串用来接收表中输入信息
                   string pub_id;
                string sup_id;

                string book_id = txtBookID.Text.Trim();

                string book_name = txtBookName.Text.Trim();
               
                string price;
                if (txtCostPrice.Text.Trim() != "")
                    price = txtCostPrice.Text.Trim();
                else
                    price = null;
               
                string quan;
                if (txtQuantity.Text.Trim() != "")
                    quan = txtQuantity.Text.Trim();
                else
                    quan = null;

                string sale_price;
                if (txtSalePrice.Text.Trim() != "")
                    sale_price = txtSalePrice.Text.Trim();
                else
                    sale_price = null;

                string otherInfo;
                if (richtxtInfo.Text.Trim() != "")
                    otherInfo = richtxtInfo.Text.Trim();
                otherInfo = null;

                try
                {
                    //根据type_name获得type_id
                    string selectString1 = "select type_id from bookTypes where type_name = @type_name";
                     = selectString1;
                    sc.Parameters.Add(new SqlParameter("@type_name", cbbBookType.SelectedItem.ToString()));
                    string type_id = sc.ExecuteScalar().ToString();

                    //根据pub_name获得pub_id
                    if (cbbPubisher.SelectedItem != null)
                    {
                        string selectString2 = "select pub_id from publishers where pub_name = @pub_name";
                         = selectString2;
                        sc.Parameters.Add(new SqlParameter("@pub_name", cbbPubisher.SelectedItem.ToString()));
                        pub_id = sc.ExecuteScalar().ToString();
                    }
                    else
                        pub_id = null;

                    //根据sup_name获得sup_id
                    if (cbbSupplier.SelectedItem != null)
                    {
                        string selectString3 = "select sup_id from suppliers where sup_name = @sup_name";
                         = selectString3;
                        sc.Parameters.Add(new SqlParameter("@sup_name", cbbSupplier.SelectedItem.ToString()));
                        sup_id = sc.ExecuteScalar().ToString();
                    }
                    else
                        sup_id = null;                    

                    //执行插入语句
                        string insertString = "insert books (book_id,book_name,type_id,sup_id,sup_date,price,notes,unitsInStock,sale_price,pub_id,stock) values(@book_id,@book_name,@type_id,@sup_id,@sup_date,@price,@notes,@unitsInStock,@sale_price,@pub_id,@stock)";
                     = insertString;
                    sc.Parameters.Add(new SqlParameter("@book_id", book_id));
                    sc.Parameters.Add(new SqlParameter("@book_name", book_name));
                    sc.Parameters.Add(new SqlParameter("@type_id", type_id));
                    sc.Parameters.Add(new SqlParameter("@sup_id", sup_id));
                    sc.Parameters.Add(new SqlParameter("@sup_date", dtpickerStockTime.Value.Date));
                    sc.Parameters.Add(new SqlParameter("@price", price));
                    sc.Parameters.Add(new SqlParameter("@notes",otherInfo));
                    sc.Parameters.Add(new SqlParameter("@unitsInStock", quan));
                    sc.Parameters.Add(new SqlParameter("@sale_price", sale_price));
                    sc.Parameters.Add(new SqlParameter("@pub_id", pub_id));
                    sc.Parameters.Add(new SqlParameter("@stock", quan));
                    int i = sc.ExecuteNonQuery();

                    dr = MessageBox.Show("已向数据库中成功插入该图书信息！", "提示信息", MessageBoxButtons.OK, MessageBoxIcon.Information);


向bookStore中的books表中插入图书信息
其中表books中的book_id,book_name,type_id,unitsInStore,sale_price字段可以为null
为什么当输入price的文本框中没有输入任何信息时，向数据库中插入信息不成功，提示“被准备语句'(@type_name nvchar(2),@pub_name nvchar(2),@sup_name nvchar'需要参数@price,但未提供该参数”

哪个大大帮忙看看撒

看是看了啊`
 但是 不怎么懂啊`

你写数据库中的字段里参数和你给的的参数不一致....你好好看看..
你这样会不会太烦了,,用个存储过程写不更好些,,,

学习，帮LZ顶一下

sc.parameters[N].value=......

try{}
catch{}

Insert 的时候,数值型的不能为空值,你可以试着默人Price为0