Suggest you exercise the DATA step - recommend adding the line:
PUTLOG _ALL_;
so you can see the SAS variables at any given point in the DATA step portion of the program.
Also, your SAS log will likely have some tell-tale diagnostic NOTE, WARNING or ERROR messages for you to review and possibly debug, for example - given your code, I expect you will have a note:
NOTE: VARIABLE A IS UNINITIALIZED
and you will see from the PUTLOG that the named variable does not have an assigned value -- because of your assignment line.
And given that you likely want an observation for each A1 value, you will need to code a DO / END loop to bump through the array, and issue an OUTPUT statement within the DO loop.
Scott Barry
SBBWorks, Inc.