topic Re: why do we need % in front of syntax inside a macro? in SAS Programming

why do we need % in front of syntax inside a macro?

somebody — Mon, 03 Dec 2018 08:55:54 GMT

Why do we need % in front of some syntax keyword such as do, end, for, put ...etc... when inside a macro? I tried without the % and it works fine.

Re: why do we need % in front of syntax inside a macro?

Kurt_Bremser — Mon, 03 Dec 2018 09:08:31 GMT

% and & are the so-called "macro triggers", which instruct SAS to hand over the interpretation of the next item to the macro preprocessor.

"do" and "%do" are NOT the same. "do" is a data step statement, "%do" is a macro statement, no matter if they are used in a macro or in open code.

If you supply your code that "worked" with and without %, I can explain why that happens.

Re: why do we need % in front of syntax inside a macro?

RW9 — Mon, 03 Dec 2018 09:16:04 GMT

This is a misunderstanding of what macro is and how it works.

Macro is a text generator, a find/replace system if you will. The text of your program is fed into the macro pre-processor which does a find replace all occurrences of macro variables by pattern & -- ., and replaces those with the value in the macro variable. It then expands any macro code indicated by the %.

Out of that process you then have the full plain Base SAS code which then goes into the compiler to be executed. Therefore if you had:

%macro something ();
  %do i=1 %to 3;
    a=1;
  %end;
%mend something ();

Then then macro pre-processor knows that the %do loop is its part to expand the text out e.g. this will create after being through the macro pre-processor:

a=1;
a=1;
a=1;

Repeat the text 3 times.

If you replaced that with no % as:

%macro something ();
  do i=1 to 3;
    a=1;
  end;
%mend something ();

This would put in the text file:

do i=1 to 3;
  a=1;
end;

Note that in this instance the macro pre-processor is not doing the loop, it just generates that text. When this code is fed into the compiler within a datastep then the loop is executed.