title;

/**************************************************
We read in some data and implement a check that
the start date occurs before the end date.
Note the use of informat and format.
**************************************************/
data temp;
input id start end;
informat start end ddmmyy6.;
format start end date8.;
if start gt end then
 put 'ERROR: end before start: ' id= start= end= ;
cards;
1 281165 070599
2 230489 120193
3 011295 181089
4 020773 010399
;
run;

/**************************************************
When deleting observations or transforming variables
it if often useful to list the observations affected.
Note the syntax for specifying a constant date.
**************************************************/
data new;
set temp;
if start lt '01JAN70'd then do;
  put 'WARNING: observation deleted: ' id= start= end= ;
  delete;
end;
run;