It is not necessary to use loop. First sort your data using
PROC SORT data=yourdata out=newdata;
    by ID KEY CYCLE;
run;

Second, in a DATA step,
DATA finaldata(drop=(CYCLEold));
   set newdata(rename=(CYCLE=CYCLEold));
   by ID KEY CYCLEold;
   retain CYCLE;
   if first.ID then CYCLE=0;
   CYCLE + 1;   
run;

Hope it is useful.