C#

System.InvalidOperationException: 'Collection was modified; enumeration operation may not execute.'

foreach (Form frm in fc)

FormCollection fc = Application.OpenForms;
            foreach (Form frm in fc)
            {
                if (frm.Name == "Chart")
                {
                    MessageBox.Show("The form is open","error",MessageBoxButtons.OK,MessageBoxIcon.Error);
                }
                else
                {
                    Chart myCharts = new Chart();
                    myCharts.Show();
                }
            }

I am creating a book site for that, I have created dynamic buttons so that if on a particular category is clicked then that row will be fetched from the database and required information will be displayed. Now I want that if the user clicks on any particular book then the data of that book should be displayed in another panel and the current panel should hide.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Web.UI.HtmlControls;

namespace WebApplication1
{

<pre>
public partial class Genre : System.Web.UI.Page
{

    private int num;
    SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);<br />
    protected void Page_Load(object sender, EventArgs e)
    {
        Label1.Text = "Romance";
        Panel2.Visible = false;

        con.Open();
        String SQL = "Select * from Book_List where Book_category='" + Label1.Text + "'";
        SqlDataAdapter da = new SqlDataAdapter(SQL, con);
        DataSet ds = new DataSet();
        DataTable dt = new DataTable();
        da.Fill(ds);
        num = ds.Tables[0].Rows.Count;
        HtmlGenericControl Book = new HtmlGenericControl("div");
        Book.Attributes.Add("class", "books");
        Panel1.Controls.Add(Book);

        for (int i = 1; i < num; i++)
        {
            HtmlGenericControl myDiv = new HtmlGenericControl("div");
            myDiv.Attributes.Add("class", "myDiv");
            ImageButton image = new ImageButton();
            image.ImageUrl = ds.Tables[0].Rows[i]["Book_image"].ToString();
            image.CssClass = "Img";
            image.Click += new ImageClickEventHandler(this.image_Click);
            HtmlGenericControl content = new HtmlGenericControl("div");
            content.Attributes.Add("class", "content");
            Label name = new Label();
            name.CssClass = "name";
            name.Text = ds.Tables[0].Rows[i]["Book_name"].ToString();
            Label cost = new Label();
            cost.CssClass = "cost";
            cost.Text = "<br/> Rs " + ds.Tables[0].Rows[i]["Book_cost"].ToString();
            Button wishlist = new Button();
            wishlist.CssClass = "wishlist";
            wishlist.Text = "ADD TO WISHLIST";
            Book.Controls.Add(myDiv);
            myDiv.Controls.Add(image);
            myDiv.Controls.Add(content);
            content.Controls.Add(name);
            content.Controls.Add(cost);
            content.Controls.Add(wishlist);

        }

    }
    protected void image_Click(object sender, ImageClickEventArgs e)
    {
        ImageButton image = sender as ImageButton;
        Panel2.Visible = true;
        Panel1.Visible = false;            
    }
   </pre>