请教：sasbase123题中一题不懂

shiyiming

data set named month has one observation per month for each of five years for a total of 60 observation.
code:
data total;
set month;
retain month{12};
array month{12};
do i = 1 to 12;
        month{i} = sales;
end;
cnt + 1 ;
month{cnt} = sales;
run;

have syntax errors .why?