Probably easy lisp question

Hi,
i don't know if this mailing list is also for problems which are concerning ansi common lisp.
I want to convert a number into a string.

(defun makestrvar (x)
 .....
)

should evalutate to

(makestrvar 3) -> "var3"
(makestrvar 1000) -> "var1000"

I could not find a suitable function to convert a number to a string. It would be great if someone can help me.

Thanks in advance,
 Jochen