Date:         Sat, 13 Sep 2008 22:00:05 -0400
Reply-To:     Jerry <i89rt5@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Jerry <i89rt5@GMAIL.COM>
Subject:      why this "DO WHILE NOT" cause infinite loop?

Hi,

With the code below(DO UNTIL approach), I can produce the following 2 lines
in the log

Sex=F Name=Mary
Sex=M Name=William

/*****DO UNTIL approach************/
proc sort data=sashelp.class out=class; by sex name; run;

data test1;
 do until (end1);
  DO UNTIL (last.sex);
   set class end=end1;
   by sex;
  end;
  output;
  put sex= name=;
 end;
stop;
run;
/*****************/


But with the code (DO WHILE NOT approach) below, it cause an infinite loop:
produce the infinite lines of "Sex= Name=" in the log

/******DO WHILE NOT approach***********/
proc sort data=sashelp.class out=class; by sex name; run;

data test1;
 do until(end2);
  DO WHILE (NOT last.sex);
   set class end=end2;
   by sex;
  end;
  output;
  put sex= name=;
 end;
stop;
run;
/*****************/

I'm using SAS 9.1.3 sp4.

Could anyone please explain why the infinite loop is happening with the DO
WHILE NOT approach? I thought DO WHILE NOT is equivalent to DO UNTIL.

Thanks.