Error in foreach loop for Dataset -- Please help

using System;
using System.Data;
using System.Data.SqlClient;
namespace PublicTest
{
 ///

 /// Summary description for Class1.
 ///

 class myClass
 {

  ///

  /// The main entry point for the application.
  ///

  [STAThread]
  static void Main(string[] args)
  {
   //
   // TODO: Add code to start application here
   //
   string strCon = "Server=LOGICON-SERVER1,1433;Database=pubs;integrated security=SSPI;persist security info=False;Connection Timeout=10000;";
   string strSQL = "Select au_fname, au_lname, phone from authors where city = 'Oakland'";
   
   SqlConnection myCon = new SqlConnection(strCon);
   SqlCommand myCom = new SqlCommand(strSQL, myCon);

   SqlDataAdapter da = new SqlDataAdapter(myCom);
   DataSet ds = new DataSet();      
   da.Fill(ds, "authors");
      
   foreach (DataColumn dc in ds.Tables(0).Columns)
   {
    Console.Write("{0,15}", dc.ColumnName);
   }
      
  }
 }
}

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Thanks & Regards,
Ravi