列表在每个循环后变为null

Question

public class WebRole : RoleEntryPoint
{
    public struct countries
    {
         public const double usa = 94.2;
         public const double canada = 85.63;            
    }

    public List<Tuple<string, string, double>> people = new List<Tuple<string, string, double>>(); //table, userID, distance
    string[] connarr = { "SELECT UserID FROM [0971880107_0];", "SELECT UserID FROM [0971880107_1];" };

    public override bool OnStart()
    {

        // For information on handling configuration changes
        // see the MSDN topic at http://go.microsoft.com/fwlink/?LinkId=166357.
       // sqlconn();

        foreach (string s in connarr)
        {
            get_loc_age(retrieve_value(s) , s);  //s =table name, return users in table as list
        }
        return base.OnStart();

    }

    public List<string> retrieve_value(string s)  //returning users for "Item A Eval X"
    {
        string connectionString = null;
        connectionString = @"Data Source=192.168.1.222, 1433;Initial Catalog=dbs1;User ID=pratikkcn;Password=abc123";
        SqlConnection cnn;
        cnn = new SqlConnection(connectionString);
        SqlCommand comm = new SqlCommand(s, cnn);

        try
        {
            cnn.Open();
            SqlDataReader reader = comm.ExecuteReader();
            List<string> str = new List<string>();
            int i = 0;
            while (reader.Read())
            {
                str.Add(reader.GetValue(0).ToString().Trim(new Char[] { '"' }));
            }
            reader.Close();
            return str;   
        }
        catch (Exception)
        {
            throw;
        }
        finally
        {
            cnn.Close();
        }
    }

    public void get_loc_age( List<string> str , string s)
    {
        string connectionString = null;
        connectionString = @"Data Source=192.168.1.222, 1433;Initial Catalog=book_rating_dataset;User ID=pratikkcn;Password=abc123";
        SqlConnection cnn;
        cnn = new SqlConnection(connectionString);
        try
        {
            cnn.Open();
            foreach (var userid in str)
            {
                SqlCommand comm = new SqlCommand("SELECT Location, Age FROM [Users_cleaned] where UserId = '"+ userid +"'"  , cnn);
                double[] dummy = { 5.0, 5.0 }; // dummy variable
                SqlDataReader reader = comm.ExecuteReader();
                double p= 0.0 ,a = 0.0;
                string l = "";
                while (reader.Read())
                {
                    if (reader.IsDBNull(0))
                    {
                        l = null;//location
                        a = 0.0;
                    }
                    else
                    {
                        l = reader.GetString(0);
                        a = Convert.ToDouble(reader.GetString(1));  //age
                    }                        
                    #region countries_switch
                    switch (l)
                    {
                        case "usa":
                            p = countries.usa;
                            break;
                        case "canada":
                            p = countries.canada;
                            break;                            
                    }
                      #endregion
                }
                reader.Close();
                double[] x1 = { a, p };
                double x2 = EuclideanDistance(x1, dummy);  //distance
                people.Add(new Tuple<string, string, double>(s, userid, x2));                


var c = people.OrderBy(x => x.Item3).ToList();  //show properly ordered list here
                }
                var c = people.OrderBy(x => x.Item3).ToList();  //c get null here

        }
        catch (Exception)
        {
            throw;
        }
        finally
        {
            cnn.Close();
        }

    }

在函数get_loc_age()的foreach循环结束后，我想获得c的值，但它显示null。但是，如果我试图在foreach中获得c，它显示价值很好。此代码是从webrole的start方法调用的。我究竟做错了什么。任何线索。