How to use 'Eval'operator in code behind?

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ASP.NET

Hi,
I am working on a program which should redirect to specific page according to the user logged in.my program consisting of 4 types of users.if the user is of type "user" the program should redirect him to his viewpage.that is he can view only his details.since there are multiple users in the program,each user is identified by his userid which is unique.

following is the code i wrote to redirecting to the user's page using 'Eval'.

'str' is a string which holds the value returned by the function.(i wrote one function to determine the type of user).i am checking if the user is of type "user",then getting the corresponding userid which is unique,from the database and redirecting to view page.here since i used eval.its giving me error in the last line like "Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control."

if (str == "user")
{
  SqlConnection con = new SqlConnection();
  SqlCommand cmd = new SqlCommand();
  con = new SqlConnection(@"Data Source=CSZ-PCS43132\SQLEXPRESS;Initial Catalog=test;Integrated Security=True");
  con.Open();
  var query = "SELECT userid FROM logins2 WHERE loginid = @loginid AND password1 = @password AND usertype = " + str ;
  cmd = new SqlCommand(query, con);
  cmd.Parameters.AddWithValue("@loginid", txtusername .Text );
  cmd.Parameters.AddWithValue("@password",txtpassword .Text );
  cmd.ExecuteNonQuery();  
                
  Response.Redirect("LocalHRviewdetails.aspx?ID="+ Eval(query));
}

Can anyone pls help me?