Hello @PierreYvesILY,
You could pick one of the WEEK... informats and use the MONTH, INPUT, CATS and PUT functions to compute the month from week number and year.
Example:
data test;
do week=26 to 27;
do year=2019 to 2021;
mon=month(input(cats(year,'W',put(week,z2.)),weekv.));
output;
end;
end;
run;
Result:
week year mon
26 2019 6
26 2020 6
26 2021 6
27 2019 7
27 2020 6
27 2021 7
In this example the month is (by default) calculated for the Monday of the respective week.