DB Connection

I think what you really want to do is create a static db connection class that that all your code behind classes have access to.
For example: (Please note that I just hammered this code into here without testing it, so there are likely typos and errors, but I think it gives you the idea. It is also incomplete in that you will want to handle disposing it and such at some point.

sealed class DatabaseConnectivity
{
    private static SqlConnection _dbConn = null;

    public static SqlConnection GetConnection()
    {
        if( _dbConn == null )
            _dbConn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\Guru\HRP\App_Data\hrp.mdf;Integrated Security=True;User Instance=True"); 

        if( _dbConn.State == ConnectionState.Closed )
            _dbConn.Open();
    }

    return _dbConn;
}

Once you have a class like this, then all you have to do is call it from whichever form uses it.

If you are using win forms, see here[^].

Here is a google search that gives you instructions on how to achieve this:
Google[^]

If you are creating a WPF application: Data Binding Overview[^]

Update 1:

Based on your connection string I assume that you are working on an ASP.Net application.

You'll probably want to use the databinding features of asp.net.

SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=D:\Guru\HRP\App_Data\hrp.mdf;Integrated Security=True;User Instance=True");

Here is one article here on CP Mastering ASP.NET DataBinding[^] that you may find useful,

This Google search[^], provides you with a ton of reading material.

Example from documentation[^]:

private static void ReadOrderData(string connectionString)
{
    string queryString = 
        "SELECT OrderID, CustomerID FROM dbo.Orders;";
    using (SqlConnection connection = new SqlConnection(
               connectionString))
    {
        SqlCommand command = new SqlCommand(
            queryString, connection);
        connection.Open();
        SqlDataReader reader = command.ExecuteReader();
        try
        {
            while (reader.Read())
            {
                Console.WriteLine(String.Format("{0}, {1}",
                    reader[0], reader[1]));
            }
        }
        finally
        {
            // Always call Close when done reading.
            reader.Close();
        }
    }
}

Usually you don't want to reuse the same connection object instance. Create a new SqlConnection on each request.

Regards
Espen Harlinn