AND OR NOT expressions logical way of writing correction please?

[Andygray]

Hi, I would like to know what is the correct way to write or in other words use AND OR NOT operators in SAS?

Let's us suppose we have 3 variables with names A B C in a dataset

/*which way of syntax is correct*?*/

if missing(a) or missing(b) and missing(c) then.....  is this correct? or

if (missing(a) or missing(b)) and missing(c) then......is is correct, meaning with the parenthesis?

another condition:

if missing(a) and missing(b) and missing(c) then......is this correct? or

if (missing(a) and missing(b)) and missing(c) then...is is correct, meaning with the parenthesis?

Please clarify the need for parenthesis. Thanks

[Reeza]

You need to define CORRECT. 

All will work but may generate different results so it depends on what you're looking for.

[Andygray]

I am just trying to learn and understand by asking how the condition is checked with and without parentheses and how the results differ. Thanks

[Reeza]

There is also documentation on the Order of Operations in Compound Expressions:

SAS(R) 9.2 Language Reference: Concepts, Second Edition

[Tom · Accepted solution]

Try it and see.

%let tests=

a and b or c

|(a and b) or c

|a and (b or c)

|a or b and c

|(a or b) and c

|a or (b and c)

;

%macro xx ;

data xx;

do a=0,1 ;

  do b=0,1;

   do c=0,1;

     put (a b c) (=);

%do i=1 %to %sysfunc(countw(&tests,|));

     testn=&i;

     test= "%scan(&tests,&i,|)";

     val= %scan(&tests,&i,|);

     put (testn test val) (=);

     output;

%end;

   end; end; end;

run;

%mend xx;

%xx;

[Andygray]

Beautiful. That clears all my doubts in my brain. Thanks Tom!

[TomKari]

Personally, I make it a habit to use parentheses to clarify the order that I want for the evaluation, even if it matches the order without parentheses. This is for two reasons; first, different languages use different rules, and it's easy to make a mistake, and second, when someone else is looking at the code, they may not know the correct rules, and may mistake what the code is doing.

On the other hand, I don't see any downside to using extra parentheses to make is explicitly clear.

Tom