Visit in Window???

data window;
set draft;
by usubjid visitnum;

if visitday ne . & visitday lt 0 then day= 0;
else day= visitday;
*bringing the preceding day using lag function;
preday=lag(day);
*identifying observation through lag of usubjid;
lagusid = lag(usubjid);
*(day-preceding day) gives the day difference;
if usubjid = lagusid then do;
if day ne . & preday ne . then daydiff=(day-preday);
end;

*VISIT WINDOW FOR SCREENING;
if day ne . & visitnum in (1) then do;
if day le 0 then viwind = 'Yes';
else viwind = 'No';
end;
*VISIT WINDOW FOR VISIT 1 2 & 3;
if daydiff ne . & visitnum in (2,3,4) then do;
if 5 le daydiff le 7 then viwind = 'Yes';
else viwind = 'No';
end;
*VISIT WINDOW FOR END OF STUDY;
if daydiff ne . & visitnum in (5) then do;
if 0 le daydiff le 1 then viwind = 'Yes';
else viwind = 'No';
end;
*VISIT WINDOW FOR FOLLOW-UP;
if daydiff ne . & visitnum in (6) then do;
if daydiff le 25 then viwind = 'Yes';
else viwind = 'No';
end;

run;