%let macro and %eval do I need double ampersand or something else?

[DougHold]

%let CPI2017 = 110; 
%let Y = 2020;

Data _null_;
%put CPI in 2017 is &CPI2017;
%put CPI in %eval(&Y-3) is &CPI%eval(&Y-3);

Why does the second put statement not produce the same result as the first one (I get a warning)? I thought maybe I need double ampersand, like this.

%put CPI in %eval(&Y-3) is &&CPI%eval(&Y-3);

But that also doesn't work, I still only get "CPI in 2017 is &CPI2017".

What I want is "CPI in 2017 is 110", just like the first statement.

[ballardw]

I think the %eval is leaving SAS looking for a simple &cpi variable, which you don't have.

If you remove the %eval this way

%let t=%eval(&Y-3);
%put CPI in %eval(&Y-3) is &&CPI&t;

Yields

CPI in 2017 is 110

[DougHold]

Good suggestion, thanks that works too.

[Quentin · Accepted solution]

Hi,

Double (or triple) ampersands can't help you here.  I often think they will, but they can't help you build a macro token when part of the token comes from executing a macro.

One way to get what you want is to use %unquote().  Unquote can also be used to 'glue' text together to make a single token, e.g.:

1    %let CPI2017 = 110;
2    %let Y = 2020;
3
4    %put CPI in 2017 is &CPI2017;
CPI in 2017 is 110
5    %put CPI in %eval(&Y-3) is %unquote(%nrstr(&CPI)%eval(&Y-3));
CPI in 2017 is 110

So %nrstr() is used above to mask the &, then %eval() executes, then %unquote unmasks the & and &CPI2017 resolves.

[DougHold]

Thank you, this is what I was looking for.

[Tom]

Don't do that. Macro language is complex enough, it not worth trying overcomplicate things just to save a line of code.

Use the %EVAL() to generate a new variable. 

Either one with the NAME of the macro variable you want.

Or one with the YEAR value you want.

1031  %let name=CPI%eval(&y-3);
1032  %put CPI in %eval(&Y-3) is &&&name;
CPI in 2017 is 110
1033  %let year=%eval(&y-3);
1034  %put CPI in %eval(&Y-3) is &&CPI&year;
CPI in 2017 is 110