SAS Global date comparison - sas

Question

I'm trying to do a date comparison but I'm not getting the correct results. Does anyone know what's going on?
%macro ttt;
%let check_start = 28APR2014;
%if "&check_start."d < "25may2014"d %then %let true = 1;
%else %if "&check_start."d > "25may2014"d %then %let true = 2;
%put &true;
%mend;
%ttt;
14 %macro ttt;
15 %let check_start = 28APR2010;
16 %if "&check_start."d < "25may2014"d %then %let true = 1;
17 %else %if "&check_start."d > "25may2014"d %then %let true = 2;
18 %put &true;
19 %mend;
20 %ttt;
true = 2
Macro-variable true should equal 1

Answer 1

You need to use %sysevalf() to evaluate the comparison in this case. The following works.
%macro ttt;
%let check_start = 28APR2015;
%if %sysevalf("&check_start"d < '25may2014'd) %then %let true=1;
%else %if %sysevalf("&check_start."d > '25may2014'd) %then %let true=2;
%put &true.;
%mend;
%ttt;

Answer 2

Reeza has provided a good solution but I thought I'd add a few suggestions as well.
The problem you are having is the reason I recommend never using date literals when working in the macro language. Instead, of date literals (i.e. "01jan2000"d) I recommend using macro variables that contain date values (i.e. %let start_of_21st_century = %sysfunc(mdy(1,1,2000)); ). By using macro variables, not only do you avoid your above issue, but you also get the benefit of being able to self-document your code.
Currently I have no idea what significance the 25th May 2014 has in your code, but if you had this line:
%let product_launch_date = %sysfunc(mdy(5,25,2014));
... then it would be clear to anyone reading it what the significance is.
Your code would then become:
%macro ttt;
%local check_start compare_date;
%let check_start = %sysfunc(mdy(4,28,2014));
%let compare_date = %sysfunc(mdy(5,25,2014));
%if &check_start < &compare_date %then %let true = 1;
%else %if &check_start > &compare_date %then %let true = 2;
%put &true;
%mend;
There's still a few more things I'd consider changing. One thing I noticed is that if the 2 date values are equal, than true will not be assigned a value. So that should probably be remedied.
Also, in SAS, the typical concept of true/false is typically represented as follows:
A value of zero represents FALSE
Any non-zero number (including negatives) represents TRUE
So having a macro variable named true with either a value of 1 or 2 (both values would normally represent a value of true) may be confusing to some. I'd consider either renaming the macro variable, or using values of 0, and 1 (or other non-zero number).
Incorporating all of this, the macro would become something like:
%macro check_dates;
%local check_start compare_date;
%let check_start = %sysfunc(mdy(4,28,2014));
%let compare_date = %sysfunc(mdy(5,25,2014));
%let check_start_compared_higher = &check_start > &compare_date;
%if &check_start_compared_higher %then %do;
%put It was higher =) ;
%end;
%else %do;
%put It was equal to or lower =( ;
%end;
%mend;
%check_dates;
A few comments on the final macro... The macro variable named true has been replaced with a more descriptive variable named check_start_compared_higher. Because we just need a boolean value stored in it, we can simply assigning it the result of evaluating the expression &check_start > &compare_date which will return either a 0 (if false) or a 1 (if true). This is easier to read than using %if...%else... statements to do an assignment, as it is immediately clear that the line of code is simply performing an assignment and nothing more.
The line %if &check_start_compared_higher %then %do; shows how we can use the newly saved value to control program flow. Because the value in &check_start_compared_higher resolves to either TRUE or FALSE we can easily use it this way to make easy-to-read if-statements.