How to declare the data table column in c#?

Question

class details
   {

       userdetails userdetails = new userdetails();
       public string last;
       public DataTable generalinfo = new DataTable();
       public void loaddata(string [] path)
       {
          //Column were declared..............
        /*generalinfo.Columns.Add("Name");
          generalinfo.Columns.Add("Totalbike");
          generalinfo.Columns.Add("Inuse");
          generalinfo.Columns.Add("Time");*/
          lines = path;
          //do something.............
       }
}

I have a data table .I wish to declare the column for my data table.But If i declared in loaddata its creating some error.Because Loaddata is Run every time.So the Error raised. 

Error:Datacolumn were already belongs to a data table ...

How to declare it before the load data .Please solve my issue?Thanks in advance...