C#

hi all  I developing a program in c#, I have two form. in the form1 I have a texbox, label and combobox, and in the second form I have a button the name cleaning and the class clean.I need is calling me class clean with me button clean and cleaning the form 1   

DataSet ds = new DataSet();
            conn_DB();

            // Oracle Cmd Local variable
            OracleCommand Cmd = null;
            Cmd = new OracleCommand();
            Cmd.Connection = mConn;

            try
            {
                string sql = "SELECT * FROM USER_INFO WHERE USE_UID='" + userid + "'" + " AND PWD='" + userpw + "'";


                Cmd.CommandText = sql;
                OracleDataAdapter adapter = new OracleDataAdapter(Cmd);
                adapter.Fill(ds); // Sometimes happen System.InvalidOperation.Exception 

            }
            catch (OracleException e)
            {
                return null;
            }

System.InvalidOperation.Exception" 

or Exception

I'm using parallel arrays to display names and grades of students. I am stuck at displaying the arrays. I get System.String[] instead of the input value I want. This is my code what am I doing wrong:



using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Parrallel_Arrays {
    public partial class frmGrades : Form {
        String nameString = "Aaron Ben Carmelina Dorethy Erinn Karin " +
                             "Lester Mitsue Nichol Ria Sherie Zachary";
        String assignmentsString = "44 92 100 100 100 97 100 95 100 0 100 100 " +
                                   "95 95 97 90 100 95 100 100 100 100 100 75 " +
                                    "98 100 65 0 100 100 100 100 100 100 95 75 " +
                                   "85 100 0 50 100 95 90 0 80 100 100 100";
        String[] arrayNames = new String[12];
        String[,] arrayGrades = new String[4, 12];
        String[] arrayAverage = new String[12];

        public frmGrades() {
            InitializeComponent();
        }

        private void frmGrades_Load(object sender, EventArgs e) {

        }

        //Method to Fill Array
        private void FillArray(String[] name, String[,] grade) {
            String[] arrayNames = { nameString };
            String[,] arrayGrades = { { assignmentsString } };
            String[] arrayAverage = { };
            char[] separator = new char[] { ' ' };
            String[] tokens = assignmentsString.Split(separator);
            String[] token2 = nameString.Split(separator);
            foreach (String token in tokens) ;

        }

        //Method to Display Array of names and assignment grades
        private void DisplayArray(String[] nameString, String[,] assignmentsString) {
            for (int i = 0; i < nameString.Length; i++) {
                lbxDisplay.Items.Add(nameString[i] + " ");
            }

        
        }    

public void Fetch()
{
    database.Query("SELECT * FROM ws_cart_product WHERE cart_id=?cart_id;");
    database.Add("?cart_id", cart_id);

    foreach (DataRow row in database.FetchAsDataTable().Rows)
    {
        cart_id = global.ParseInt(row["cart_id"].ToString());
        if (row["product_id"] != DBNull.Value)
        {
            product_id = global.ParseInt(row["product_id"].ToString());
        }
        if (row["parent_id"] != DBNull.Value)
        {
            parent_id = global.ParseInt(row["parent_id"].ToString());
        }
        if (row["quantity"] != DBNull.Value)
        {
            quantity = global.ParseInt(row["quantity"].ToString());
        }

// Here I try to combine them
        Product product = new Product();
        product.product_id = global.ParseInt(row["product_id"].ToString());
        product.Fetch();
    }
}

public void Fetch()
{
    StringBuilder query = new StringBuilder();
    query.Append("SELECT *,  ");
    query.Append("(");
    query.Append("SELECT thumbnail ");
    query.Append("FROM ws_product_file, file ");
    query.Append("WHERE file.file_id=ws_product_file.file_id ");
    query.Append("AND ws_product_file.product_id=ws_product.product_id ");
    query.Append("AND file.status_id=1 ");
    query.Append("ORDER BY sortorder DESC LIMIT 0,1");
    query.Append(") ");
    query.Append("AS thumbnail,  ");
    query.Append("(");
    query.Append("SELECT mimetype ");
    query.Append("FROM ws_product_file, file ");
    query.Append("WHERE file.file_id=ws_product_file.file_id ");
    query.Append("AND ws_product_file.product_id=ws_product.product_id ");
    query.Append("AND file.status_id=1 ");
    query.Append("ORDER BY sortorder DESC LIMIT 0,1");
    query.Append(") ");
    query.Append("AS mimetype ");
    query.Append("FROM webpage, ws_product ");
    query.Append("WHERE webpage.status_id=1  ");
    query.Append("AND webpage.webpage_type_id=4 ");
    query.Append("AND ws_product.product_id=webpage.webpage_type_content_id ");
    query.Append("AND ws_product.product_id=?product_id; ");
    database.Query(query.ToString());
    database.Add("?product_id", product_id);

    foreach (DataRow row in database.FetchAsDataTable().Rows)
    {
        product_id = global.ParseInt(row["product_id"].ToString());
        if (row["parent_id"] != DBNull.Value)
        {
            parent_id = global.ParseInt(row["parent_id"].ToString());
        }
        if (row["status_id"] != DBNull.Value)
        {
            status_id = global.ParseInt(row["status_id"].ToString());
        }
        if (row["create_date"] != DBNull.Value)
        {
            create_date = global.ParseDateTime(row["create_date"].ToString());
        }
        if (row["product_no"] != DBNull.Value)
        {
} 
// There is more...
}
}

{Dotcontent.CartProduct}

  cart_id: 1
  product_id: 64
  parent_id: 0
  quantity: 2
  customer_id: 0
  guid: null


{Dotcontent.Product}

  webpage_id: 145
  website_id: 0
  status_id: 1
  url: "mode360-composer-fotostudio-fa40"
  type: null
  webpage_type_id: 0
  webpage_type_content_id: 0
  version: 0
  language_id: 0
  parent_id: 0
  related_webpage_id: 0
  title: "Mode360 Composer Fotostudio FA40"
  text: null
  short_description: null
  meta_description: null
  published_from: 1-1-0001
  published_to: 1-1-0001
  created_on: 1-1-0001
  created_by: 0
  product_id: 64
  create_date: 16-9-2016
  product_no: "291610"
  ean: ""
  price_on_request: False
  weight: 0
  brand_id: 0
  in_export: False
  template_id: 1
  mimetype: "image/jpeg"
  thumbnail: "iVBORw0KGg
  price: 0
  old_price: 0
  label: "Tijdelijke aanbieding"
  quantity: 0

CartProduct cart = new CartProduct();
       cart.cart_id = 1;
       cart.Fetch();

       Response.Write("<pre>" + ObjectDumper.Dump(cart) + "</pre>");


       Product product  = new Product();
       product.product_id = cart.product_id;
       product.Fetch();

       Response.Write("<pre>" + ObjectDumper.Dump(product) + "</pre>");