microsoft sql server multiple if else statements

Please correct my query. Want to write multiple if else in sql server and I am not sure of the syntax. Thanks!

select  SUBSTRING(CONVERT(CHAR(10), getdate(), 101),1,2) as [Current Period],
gl_account_period_summary.year_budget as [Year Budget],
case
when [Current Period] = 1 then '01/31/' + [Year Budget]
when [Current Period] =  2 then '02/28/' + [Year Budget]
when [Current Period] = 3 then  '03/31/' + [Year Budget] 
when [Current Period] = 4 then '04/30/' + [Year Budget]
when [Current Period] =  5 then '05/31/' + [Year Budget]
when [Current Period] =  6 then '06/30/' + [Year Budget] 
when [Current Period] = 7 then '07/31/' + [Year Budget]
when [Current Period] = 8 then '08/31/' + [Year Budget] 
when [Current Period] = 9 then '09/30/' + [Year Budget]
when [Current Period] = 10 then '10/31/' + [Year Budget]
when [Current Period] = 11 then '11/30/' + [Year Budget] 
when [Current Period] =  12 then '12/31/' + [Year Budget] 
else ''  
end
from gl_account_period_summary;