Number of days in month in year

 SELECT EXTRACT(DAY FROM LAST_DAY(SYSDATE)) num_of_days FROM dual;

/
SELECT SYSDATE, TO_CHAR(LAST_DAY(SYSDATE), 'DD') num_of_days FROM dual
/
-- Days left in a month --
SELECT SYSDATE, LAST_DAY(SYSDATE) "Last", LAST_DAY(SYSDATE) - SYSDATE "Days left"
FROM DUAL
/

---- Crystal Report 

---- Function

if (month(cdate({?Month(Ex:June-2019)})) in [1,3,5,7,8,10,12]) then 

31 

else if (month(cdate({?Month(Ex:June-2019)})) in [4,6,9,11]) then 

30 

else if (month(cdate({?Month(Ex:June-2019)})) = 2 and remainder(year(cdate({?Month(Ex:June-2019)})),2) = 0) then 

29 

else 

28

------

{EMP_SALARY_SHEET\\.GROSS_SALARY}/(
if (month(today) in [1,3,5,7,8,10,12]) then
     31
else if (month(today) in [4,6,9,11]) then
    30
else if (month(today) = 2 and remainder(year(today),2) = 0) then
    29
else
    28
)*{EMP_SALARY_SHEET\\.ABSENT_DAYS}