C# Class to return datatable

Hi Experts

I'm new to C# I'm writing some code to return a datatable when a user passes a sql statement to a class, it's not working though as the class want's a sting returned.

 class SQL_Array
    {

        string SQL;
        DataTable results;

         public SQL_Array()
        {

        }

        public SQL_Array(string strSQL,DataTable result )
        {
            results = result;
            SQL = strSQL;
        }

        public string SQL_Results()
        {
           // string []SQL_Results;

            string SQL = "Select * from dmt.dbo.DIT_tblBlah where txtstaffid is not null";

            SqlConnection cnnDIT = new SqlConnection("Blah");
            cnnDIT.Open();

      

            SqlDataAdapter adap = new SqlDataAdapter(SQL, cnnDIT);

          // create an empty DataTable to hold the results
            DataTable results = new DataTable();

            // populate the DataTable. Note: the SqlDataAdapter will take care of opening/closing the connection for you
            adap.Fill(results);

            cnnDIT.Close();

            return results;

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