SAS data step for array, errors and warnings - sas

Question

I am getting the following errors/warnings:
WARNING: Apparent symbolic reference ARRAY_MONTH_COUNT not resolved.
ERROR: Too many variables defined for the dimension(s) specified for the array array1.
ERROR 22-322: Syntax error, expecting one of the following: an integer constant, *.
ERROR 200-322: The symbol is not recognized and will be ignored.
for the following code:
data demo_effective;
set work.demo;
array array1 [&array_month_count] $ 1 membsdemo_flag_&start_yrmo
membsdemo_flag_&end_yrmo;
length yrmo 6;
do i=1 to &array_month_count;
if array1[i] = 'N' then continue;
if array1[i] = 'Y' then yrmo = substrn(vname(array1[i]),20,6);
output;
end;
run;
I didn't write this program, I am just trying to work with it, so I don't know why this isn't working (I made no changes, just ran the program in SAS and it was already broken), and I am still learning SAS and SQL, so half of this program is nonsense to me even after watching some videos and trying to find more information about it.
If it helps, it looks like the warning/errors are occurring around array1 [&array_month_count].

Answer 1

&array_month_count is a macro variable. In SAS, this is a string that is substituted at compile time. Macros "write" code.
It looks like all the errors you are getting are because that variable does not have a value.
So somewhere in the code, there should be something that sets the value of array_month_count. Find that, fix it, and this step should work.

Answer 2

A bit more detail than Dom's answer may be helpful, though his answer is certainly the crux of the issue.
&array_month_count needs to be defined, but you also probably have a few other issues.
array array1 [&array_month_count] $ 1 membsdemo_flag_&start_yrmo
membsdemo_flag_&end_yrmo;
This is probably wrong, or else this code is perhaps doing something different from what it used to: I suspect it is intended to be
array array1 [&array_month_count] $ 1 membsdemo_flag_&start_yrmo - membsdemo_flag_&end_yrmo;
In other words, it's probably supposed to expand to something like this.
array array1 [6] $ 1 membsdemo_flag_1701 membsdemo_flag_1702 membsdemo_flag_1703 membsdemo_flag_1704 membsdemo_flag_1705 membsdemo_flag_1706;
The 6 there isn't actually needed since the variables are listed out (in a condensed form). The dash tells SAS to expand numerically with consecutive numbers from the start to the end; it would only work if your yrmo never crosses a year boundary. It's possible -- is appropriate instead - it tells SAS to expand in variable number order, which works fine if you have consecutively appearing variables (in other words, they're adjacent when you open the dataset).
The 6 is however needed for the second bit.
do i=1 to &array_month_count;
Unless you rewrite it to this:
do i = 1 to dim(array1); *dim = dimension, or count of variables in that array;
In which case you really don't even need that value.
--
If it's actually intended to be the code as above, and only have 2 variables, then you don't need &array_month_count since it's known to be only 2 variables.