I'm new to macro programming. In the last week or so, I have posted two questions about macros. The responses to those questions have greatly enhanced my understanding of when and how to use macros. They also raised a few questions, which I'm asking here. I believe this information would be very useful to all "macro newbees," not just to me. Let me use some code from a previous question as a reference:

*** Specify a set of years; %LET A = 1997; %*Set start year; %LET B = %EVAL(&A +1); %LET C = %EVAL(&A +2); %LET D = %EVAL(&A +3); %LET E = %EVAL(&A +4); %LET F = %EVAL(&A +5);

%MACRO RDCTAP; %DO X=&A %TO &F;

DATA T&X; INFILE TAP&X; INPUT @10 GRDT&X 2. @17 LVLT&X 2. @19 STBL&X $1. @20 SPC_CODE $3. @24 BILIND 1. @29 LEPCD 1. @72 SID 8. @166 RPR&X 2. @635 ACCOM 1. @698 UNT&X 4.; IF RPR&X < 25 THEN Q&X=1; ELSE Q&X=2; RUN; PROC PRINT DATA=T&X (OBS=5); %END; %MEND RDCTAP; %RDCTAP

1) Ian Whitlock advises against using global variables. He prefers parameters. I can see where the use of parameters is tighter and cleaner. But here's where I see an advantage to global variables: I like to have a "Declarations" section at the beginning of my program that acts like a menu. I can use global variables like "switches." I can change the schools I include in an analysis, the grades, the years of test scores, whether to include or exclude special ed populations --all from one place. With parameters, I would need to page through the program to find and change the specifications for each macro. Does that seem like a valid design consideration?

2) I'm still not completely clear about the distinction between macro variables and data step variables. In the sample code, obviously variables created with a %LET statement are macro variables. I think the index variable X, created in "%DO X=&A %TO &F;" is a macro variable. But what about RPR&X? As I understand it, RPR&X is created in a data step; so it has to be a data step variable. &X is a macro variable that contributes to labeling the data step variable (e.g., RPR1997, RPR1998, etc). Does this comply with the directive from the SAS Guide To Macro Processing, "You can define and use macro variables anywhere in a SAS program, except within data lines"? It seems to me that &X is being defined outside the data step but used within data lines.

If anyone has any thoughts on these issues, I would appreciate hearing from you.

Regards, Tony P.

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