Write the syntax to create a Function in SQL

Below is the syntax to create a Function in SQL:

Create [or Replace] Function [Schema.]FunctionName
(argument [in|out] datatype])
return datatype
is
[variables if any]
begin
[Statements...];
return [return value];
end;

See example below:

Create or Replace IsEligibleToVote(InputAge in number )
return varchar2
is
    v_name t_citizen.varchar2%type;
    v_age t_citizen.varchar2%type;
    v_eligible varchar2 = 'no';
begin
   if(InputAge > 18) then
     v_name = &&inp1;
     v_age = &&inp2;
     insert into t_citizen values (v_name, v_age) ;
     v_eligible='yes';
    end if;
    return v_eligible;
end;