Asp.net login script
<p>i'm new to asp.net, i'm writing a login &amp; registration script for learning database application. But the script seems not work. it stills can add duplicated username. Here is the script</p>

<pre><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;

public partial class Registration : System.Web.UI.Page
{
    static string temp;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["earchConnectionString"].ConnectionString);
            con.Open();
            string cmdStr = "Select count(*) from [user] where UserName='" + TextBoxUN.Text + "'";

            SqlCommand userExist = new SqlCommand(cmdStr, con);
            int temp = Convert.ToInt32(userExist.ExecuteScalar().ToString());

            con.Close();
            if (temp == 1)
            {
                Response.Write("User Name Already Exist....&lt;br /&gt; Please Choose Another User Name.");
            }
        }

    }
    protected void Submit_Click(object sender, EventArgs e)
    {

        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["earchConnectionString"].ConnectionString);
        con.Open();
        string insCmd = "Insert into [user] (UserName, Password, EmailAddress, FullName, level) values (@UserName,@Password,@EmailAddress, @FullName, @level)";
        SqlCommand insertUser = new SqlCommand(insCmd, con);
        insertUser.Parameters.AddWithValue("@UserName", TextBoxUN.Text);
        insertUser.Parameters.AddWithValue("@Password", TextBoxPass.Text);
        insertUser.Parameters.AddWithValue("@EmailAddress", TextBoxEA.Text);
        insertUser.Parameters.AddWithValue("@FullName", TextBoxFN.Text);
        insertUser.Parameters.AddWithValue("@level", level.SelectedValue.ToString());

        try
        {
            insertUser.ExecuteNonQuery();
            con.Close();
            //Response.Redirect("Login.aspx");
            Label1.Text = temp;
        }
        catch (Exception er)
        {
            Response.Write("Something wrong");
        }
        finally
        {
            //Any Special Action You Want To Add
        }

    }
}
</code></pre>

<p>Any can detect the problems?</p>

<p>thanks</p>
