delphi中错误 incompatible types: 'string' and 'TEdit'

初学者 出现错误incompatible types: 'string' and 'TEdit'请教高手指点一二！procedure TForm_usergl.btnaddClick(Sender: TObject);
var
  sex,sql:string;
begin
  sex:='男';
  if rb_woman.Checked then sex:='女';
  sql:='insert into student(stuNO,stuname,stusex,stubirth,stuaddress,classid)values('''+edt_stuNO+''','''+edt_stuname+''','''+sex+''','''+cbb_year-cbb_month-cbb_day+''','''+edt_stuaddress+''','''+GetclassidFromName(cbb_class.Text)+''')';
  ExecuteFromSQL(sql);
  LoadData;
  DM3.ADOQuery1.Last;
end;