simple macro: syntax error

[bncoxuk]

SAS said there is syntax error for &j:

%MACRO calnum;
  %DO j=1 %TO 2;
  %DO i=1 %TO 10;
     PROC UNIVARIATE DATA=work.data&j;
       VAR diff;
       OUTPUT OUT=work.pctile&j%SYSFUNC(PUTN(&i,z2.)) PCTLPRE=P&j_ PCTLPTS=1 to 100 BY 1;
     RUN;
  %END;
  %END;
%MEND;

It seemed that the use of work.data&j is fine, but it is error to specify it as: PCTLPRE=P&j_  

How can I put this right?

[Linlin · Accepted solution]

please change 

PCTLPRE=P&j_ PCTLPTS=1 to 100 BY 1; to

PCTLPRE=P&j._ PCTLPTS=1 to 100 BY 1;

[Tom]

LinLin's answer should solve the problem.  SAS will interpret &J_ as a request to expand the non existent macro variable named J_.  Placing the period after the J will let SAS know that you want to expand the value of the macro variable J instead.