if substr(date,6,2) in ("01","03","05","07","08","10", "12") then date=strip(date)||'-31';
else if substr(date,6,2) in ("04","06","09","11") then date=strip(date)||'-30';
else do;
n= input(substr(date,1,4),best.);
if (mod(n,4) ne 0) or (mod(n,100)=0 and mod(n,400) ne 0) then date=strip(date)||'-28';
else date=strip(date)||'-29';
end;

还有没有更简洁的方法？