data _caldates; set _caldates;
    n+1;
    if intnx('month',beg_date,0,'e')=
    intnx('month',"&mindate"d,0,'e') then call symput ('start',n);
    if intnx('month',end_date,0,'e')=
    intnx('month',"&maxdate"d,0,'e') then call symput ('finish',n);
  run;

  %do j=&start %to &finish %by &step;

   data _null_; set _caldates (sortedby=n where=(n=&j));
    call symput ('beg',beg_date);
   run;

  data _null_; set _caldates (sortedby=n where=(n=&j));
  call symput ('end',end_date);
   run;

   data _sample/view=_sample;
     do k=1 by 1 until (last.permno);
      set _vol; by permno;
      where &beg<=date<&end;
      if missing(ret) then continue;
      mcount=sum(mcount,1);
    end;
   keep permno mcount;
   run;

这段程序为什么用call symput 定义的 start finish beg和end好像不工作那？谢谢各位帮助