topic Re: Do Loop in SAS Programming

Do Loop

cow240 — Wed, 16 May 2018 15:57:45 GMT

data WORK.LOOP;
X = 0;
do Index = 1 to 5 by 2;
X = Index;
end;
run;

Q) Upon completion of execution, what are the values of the variables X and Index in the SAS data set
named WORK.LOOP?

The answer given is X = 5, Index = 7

Can someone kindly enlighten me?

Re: Do Loop

LinusH — Wed, 16 May 2018 16:00:01 GMT

Run the step yourself and insert PUT statements or using data step debugger to follow variable value assignments.

Re: Do Loop

novinosrin — Wed, 16 May 2018 16:02:27 GMT

Using put statements carefully between statements helps us to know what's happening during each iteration and why(logic aka the loop's exit)

data WORK.LOOP;
X = 0;
do Index = 1 to 5 by 2;
X = Index;
put x= index=;
end;
put index=;
run;

put x= index=;-->X=1 Index=1
put x= index=;-->X=3 Index=3
put x= index=;-->X=5 Index=5
put index=; -->Index=7 loops exit

Does this help at all?

Re: Do Loop

cow240 — Wed, 16 May 2018 16:05:01 GMT

Thank you for your replies. Apologies for the newbie questions as im new to SAS. I just thought that intuitively, it should stop at 5 since it exits at 5. I guess I have a lot to learn!

Re: Do Loop

novinosrin — Wed, 16 May 2018 16:07:03 GMT

@cow240wrote:
Thank you for your replies. Apologies for the newbie questions as im new to SAS. I just thought that intuitively, it should stop at 5 since it exits at 5. I guess I have a lot to learn!

No need for Apologies . There aint somebody who is more dumb than me when i started learning sas. Cheers!

Re: Do Loop

MarkWik — Wed, 16 May 2018 17:39:09 GMT

The question is very trivial and basic, however you @cow240 could mark one of the answer as accepted and answered

Re: Do Loop

mkeintz — Wed, 16 May 2018 19:28:04 GMT

The do loop

DO index=1 to 5 by 2;

x=index;

end;

tells SAS to

Assess INDEX at the top of the loop to see whether index satisfies the condition needed to run another iteration.
Increments INDEX by 2 at the bottom of the loop.

So when index=5, the loop runs an iteration (and x=5). At the end of that iteration INDEX is incremented to 7, then SAS goes to the top for assessment of index. It exceeds 5, so the do loops are finished, leaving X=5.