If you want to loop directly though the datatable, you loop through the datatable1.Rows collection that contains DataRow objects. given a DataRow, dr, you get a particular column value by indexing it with teh column name.
for(int i = 0; i < dt.Rows.Count; ++i)
{
DataRow dr = dt.Rows[i];
string val = dr["ColumnName"].ToString();
}