%macro m1(stock = );
data wk1;
     if &stock < 999    then s = trim("000"||"&stock");
else if &stock < 9999   then s = trim("00"||"&stock");
else if &stock < 99999  then s = trim("0"||"&stock");
else                          s = trim(" "||"&stock");
run;
data wk2;
set wk1;
call symput('z',s,'G');
run;
%mend m1;
%m1(stock = 875) %put &z;

不知到问题出在哪里，请高手指教，谢谢。