connection not closed error in c#?

thank you friends for all answers

Hi,
        Try like this


Regards,
Iftikar

i have insert form for inserting student info in the form i have 2 comboboxes one for college and the other for depts .... i bind the first combobox with a database column usin this methos

        private void bindcombo_college_name()
        {
            OleDbCommand com = new OleDbCommand();
            OleDbDataReader reader;
            com.Connection = db_con;
            db_con.Open();
            college_name.Items.Clear();
            com.CommandText = "select * from colleges";
            reader = com.ExecuteReader();
            while(reader.Read())
            {
                string combo_items = reader["college_name"].ToString();
                college_name.Items.Add(combo_items);//college_name is a combobox
            }
            db_con.Close();

and i want in the second combobox to display only the depts of the college that i select in the first combobox i use the first combobox textchange event to do this with this code

            OleDbCommand com = new OleDbCommand();
            OleDbDataReader reader;
            com.Connection = db_con;
            dept_name.Items.Clear();
            db_con.Open();
            com.CommandText = "select * from [depts] inner join [colleges] on [colleges].college_code = [depts].college_code where [colleges].[college_name] = '" + college_name.Text + "'";
            reader = com.ExecuteReader();
            while (reader.Read())
            {
                string combo_items = reader["dept_name"].ToString();
                dept_name.Items.Add(combo_items);//college_name is a combobox
            }
            db_con.Close();
it do the action that i want but when i click the insert button it inserts data and gives connection not closed error

use these usings

using System.Data.SqlClient;
using System.Data;

write your connection in this if block


if (db_con.State == ConnectionState.Closed)
  {
  db_con.Open();
  }