Either method should work. You should also look at the user defined function syntax as a possible solution. Please consult the documentation on 3 different methods.
drop table h1
create table h1 ( status int , c2 date )
insert into h1 values ( 1, '2000-12-12' )
insert into h1 values ( 2, '2002-01-01' )
select datediff ( day, if ( status = 1, now() , c2 ), now() ) from h1