How to assign the result value of a sql stmt to a variable in sql*plus

Question

e.g.
var v_date
var v_test :=select hour from tablename where date=v_date

Answer 1

but this piece of code doesn't work:
var in_year number
var start_date varchar2(30)
var mar_2nd_sun date
accept in_year number prompt 'Enter the year of interest>'
execute :start_date := '01-mar-' || &&in_year
print start_date
select next_day(:start_date,'sunday')+7 into :mar_2nd_sun from dual;
print mar_2nd_sun
delete from &&table_name where tdate=:mar_2nd_sun and hour=1;
Error:
old 1: delete from &&table_name where tdate=:mar_2nd_sun and hour=1
new 1: delete from tbl_datehour_test where tdate=:mar_2nd_sun and hour=1
SP2-0552: Bind variable "MAR_2ND_SUN" not declared.