[{"id":"0","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"1","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"2","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"3","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"4","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"5","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"6","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"7","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"8","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"},
{"id":"9","name":"name","active":"active","user_id":"user_id","no_of_reports":"no_of_reports"}]

      public DataTable getData()
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("id", typeof(Int32));
            dt.Columns.Add("name", typeof(string));
            dt.Columns.Add("active", typeof(string));
            dt.Columns.Add("user_id", typeof(string));
            dt.Columns.Add("no_of_reports", typeof(string));
            for (int i = 0; i < 10; i++)
            {
                dt.Rows.Add(i, "name", "active", "user_id", "no_of_reports");
            }
            return dt;
        }

     public string DataTableToJsonWithStringBuilder(DataTable table)
        {
            var jsonString = new StringBuilder();
            if (table.Rows.Count > 0)
            {
                jsonString.Append("[");
                for (int i = 0; i < table.Rows.Count; i++)
                {
                    jsonString.Append("{");
                    for (int j = 0; j < table.Columns.Count; j++)
                    {
                        if (j < table.Columns.Count - 1)
                        {
                            jsonString.Append("\"" + table.Columns[j].ColumnName.ToString()
                         + "\":" + "\""
                         + table.Rows[i][j].ToString() + "\",");
                        }
                        else if (j == table.Columns.Count - 1)
                        {
                            jsonString.Append("\"" + table.Columns[j].ColumnName.ToString()
                         + "\":" + "\""
                         + table.Rows[i][j].ToString() + "\"");
                        }
                    }
                    if (i == table.Rows.Count - 1)
                    {
                        jsonString.Append("}");
                    }
                    else
                    {
                        jsonString.Append("},");
                    }
                }
                jsonString.Append("]");
            }
            return jsonString.ToString();
        }

  DataTable dt = getData();
  string str = DataTableToJsonWithStringBuilder(dt);