topic Re: Macro Do Loop Iteration in SAS Programming

Macro Do Loop Iteration

dhana — Sun, 25 May 2014 14:29:32 GMT

All -

I knew that we can't perform arithmetic operation directly on the macro variables, if we have to perform the same then we need to use either %EVAL or %SYSEVALF macro functions.

%LET A=3;

%LET B=4;

%LET SUM=&A+&B;

%PUT SUM=&SUM.;

%LET SUM=%EVAL(&A+&B);

%PUT SUM=&SUM.;

But if you look at the below code, the do loop iterating 10 times through the %put statement without even incrementing the counter i by 1. Can anyone explain how this is happening.

%MACRO LOOPCHK;

%DO I=1 %TO 10;

%PUT I=&I;

%END;

%MEND LOOPCHK;

%LOOPCHK;

Re: Macro Do Loop Iteration

Reeza — Sun, 25 May 2014 18:53:13 GMT

You have something else wrong somewhere, all of your code above works as expected..

1 %MACRO LOOPCHK;

3 %DO I=1 %TO 10;

4 %PUT I=&I;

5 %END;

7 %MEND LOOPCHK;

9 %LOOPCHK;

I=1

I=2

I=3

I=4

I=5

I=6

I=7

I=8

I=9

I=10

10 %LET A=3;

11 %LET B=4;

12 %LET SUM=&A+&B;

13 %PUT SUM=&SUM.;

SUM=3+4

15 %LET SUM=%EVAL(&A+&B);

16 %PUT SUM=&SUM.;

SUM=7

Re: Macro Do Loop Iteration

dhana — Mon, 26 May 2014 04:55:24 GMT

Reeza,

I don't have problem with my code. My question is when we need macro functions like evalf & sysevalf to perform arithmetic operation, how the same is performed without any macro functions in %do loop macro statement.

Re: Macro Do Loop Iteration

Kurt_Bremser — Mon, 26 May 2014 07:17:22 GMT

That is just a function of the iterative %do. It does the increment implicitly.

You probably miss the constructs you would expect in a C language "for" statement. (initialize, increment, end condition)

Re: Macro Do Loop Iteration

Ksharp — Mon, 26 May 2014 13:12:22 GMT

By Default, SAS will take %DO I=1 %TO 10; I as Integer just like %DO %eval( I=1 ) %TO %eval(10) ; You can find it in Macro Documentation. if I is double or float , this wouldn't work . you need %sysevalf() around it.

Xia Keshan

Re: Macro Do Loop Iteration

stat_sas — Mon, 26 May 2014 14:39:48 GMT

Hi,

Try this, may help in understanding the concept.

Thanks,

Naeem

options symbolgen;
%MACRO LOOPCHK;
%DO I=1 %TO 10;
%PUT I=&I;
%END;
%MEND LOOPCHK;
%LOOPCHK;

options symbolgen;
%MACRO LOOPCHK;
%let I=1;
%DO %while (&I<=10);
%PUT I=&I;
%let I=%eval(&I+1);
%END;
%MEND LOOPCHK;
%LOOPCHK;

Re: Macro Do Loop Iteration

dhana — Mon, 26 May 2014 16:18:22 GMT

Thank you Ksharp, stat@sas, Reeza and KurtBremser for your replies and insight on how this implicit looping works.