// 填充参数
            SqlParameter para = cmd.Parameters.Add("@id", SqlDbType.NVarChar);
            para.Value = id;
            para = cmd.Parameters.Add("@name", SqlDbType.NVarChar); // 用具体的字段数据类型替换SqlDbType
            para.Value = name;
            para = cmd.Parameters.Add("@num", SqlDbType.NVarChar);
            para.Value = num;
            para = cmd.Parameters.Add("@price", SqlDbType.NVarChar);
            para.Value = num;
            
            //执行语句 
            cmd.ExecuteNonQuery();
            
            //关闭连接 
            conn.Close();

------解决方案--------------------
1，方法一：

C# code

 protected void Button1_Click(object sender, EventArgs e) 
    { 
        //从窗体中获取值 
        string name, id, num, price, sum; 
        name = ProName.Text; 
        id = ProID.Text; 
        num = ProNum.Text; 
        price = ProPrice.Text; 
        sum = ProSum.Text; 

        string sqlstring = "Server=localhost;uid=sa;pwd=2613000;database=Stock"; 

        System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(sqlstring); 

        conn.Open(); 

        string insertCommand = "insert into 采购单(采购单号,产品名称,库存数量,成本价格)values({0},{1},{2},{3})"; 
        System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand(string.Format(insertCommand,id,name,num,price), conn); 
        //执行语句 
        cmd.ExecuteNonQuery(); 
        //关闭连接 
        conn.Close(); 
        Response.Write(" <script>alert('写入成功!') </script>"); 
    }

------解决方案--------------------
C# code

string insertCommand = "insert into 采购单(采购单号,产品名称,库存数量,成本价格)values(@id,@name,@num,@price)"; 

// 改为：

string insertCommand = "insert into 采购单(采购单号,产品名称,库存数量,成本价格) values('" + id + "','" + name + "','" + num + "','" + price + "')";