求助？关于管长标注的程序

(defun gps_guanchang(dw / danwei el2 ent ent2 n txt txt3 txt4)
(gps_save_state)
(setq danwei dw )
(setq n 1)
(while (/= n nil)
(c:gps_osmode)
(setq txt4 (getdist "\n 点取两点起点井、终点井"))
(setq txt3 (/ txt4 danwei)) ;txt3管长
(setvar "osmode" 0)
(princ "\n 选择标注管长数字:")
(setq ent2 (car (gps_onlyselect "TEXT")))
(setq el2 (entget ent2))
(setq txt (rtos txt3 2 1))
(setq ent (subst (cons 1 txt) (assoc 1 el2) el2))
(entmod ent)
(if (= ent2 nil) (setq n nil))
);end while
(redraw)
(gps_load_state)
)
以上得程序问题出在哪里？？？