SQL number-sequence generation

When I do exercise in http://www.sql-ex.ru/learn_exercises.php#answer_ref 104(2)

table classes:

class	type	country	numGuns	bore	displacement
Bismarck	bb	Germany	8	15	42000
Iowa	bb	USA	9	16	46000
Kongo	bc	Japan	8	14	32000
North   Carolina	bb	USA	12	16	37000
Renown	bc	Gt.Britain	6	15	32000
Revenge	bb	Gt.Britain	8	15	29000
Tennessee	bb	USA	12	14	32000
Yamato	bb	Japan	9	18	65000

Questions：

For each cruiser class, make numbering (sequentially from 1) of available
guns.
Output: class name, number of a gun in the format 'bc-N'.

Answer:

the right sql:

with cte_n(num) as

(select 1  

union all  

select num+1  

from cte_n  

where num<100 )

select cs.class ,type+'-'+cast(cte_n.num as varchar(10)) as num

from classes cs join

cte_n on cte_n.num<=cs.numGuns

where type='bc'