Change macro variable with each iteration (plus and minus)

[DougHold]

I would like a macro variable that is referenced to change -1 and +1 with each iteration. For example in the following loop, each iteration from the start year of 2011 to the end year of 2013 should give the year minus 1 (YM1), the year (Y), and the year plus 1 (YP1).

%macro Loop_year(startyear=, endyear=);
   %DO I = &startyear %TO &endyear;
      %put YM1 is &I-1;   
	  %put Y   is &I;
	  %put YP1 is &I+1;
   %end;
%mend Loop_year;

%Loop_year(startyear=2011, endyear=2013);

This is what I get:

YM1 is 2011-1
Y is 2011
YP1 is 2011+1
YM1 is 2012-1
Y is 2012
YP1 is 2012+1
YM1 is 2013-1
Y is 2013
YP1 is 2013+1

But this is what I want:

YM1 is 2010
Y is 2011
YP1 is 2012
YM1 is 2011
Y is 2012
YP1 is 2013
YM1 is 2012
Y is 2013
YP1 is 2014

Would this be possible? Thanks in advance

[PeterClemmensen · Accepted solution]

Like this?

%macro Loop_year(startyear=, endyear=);
   %DO I = &startyear %TO &endyear;
      %put YM1 is %eval(&I-1);   
	   %put Y   is &I;
	   %put YP1 is %eval(&I+1);
   %end;
%mend Loop_year;

%Loop_year(startyear=2011, endyear=2013);

Result:

YM1 is 2010
Y   is 2011
YP1 is 2012
YM1 is 2011
Y   is 2012
YP1 is 2013
YM1 is 2012
Y   is 2013
YP1 is 2014

[DougHold]

Exactly, thank you! The %eval() is what I was looking for.