Problem on attach local variable with entity table substitute with dot

mcard_list mcardlist = new mcard_list();
numberoftimes = 0;
timesheet.AddTomcard_list(mcardlist);
while (numberoftimes < collectionnumbers)
{
    var FieldName = mcardlistfields[numberoftimes, 0].ToString();
    var FieldType = mcardlistfields[numberoftimes, 1].ToString();

   switch (FieldType)
  {

      case "String" :


         mcardlist. + FieldName = "Test"; <=I know wrong here but i don't know how to do.

         break;

      case "DateTime" :

         mcardlist. + FieldName = "2015-1-23"; <=I know wrong here I don't know how to do it.

         break;
  }

   numberoftimes += 1;
}
timesheet.SaveChanges();

Could Anyone help me how can add fieldname stored in variable "FieldName" for later attach with "mcardlist." (ended with dot).Thanks.