怎么将字符串进行比较

如何将字符串进行比较？
ls_qs = sle_1.text
ls_zz = sle_2.text

if ls_qs<>'' and ls_zz <>'' then
  is_newselect = is_newselect + " and " + "a.sxhh = '" + ls_sxhh + "'"
end if 

sxhh是字符型 如何进行比较

例如 sle_1.text ='0000001' sle_2.text = '9999999'

如何得出sxhh中没有在sle_1和sle_2范围内的字符？？？
比如sxhh只保存了0000001-0000010 能够得出之间没有的数？？？

------解决方案--------------------

探讨

ls_old[j] = Trim(Mid(ls_data,1,Pos(ls_data,',') - 1)))
FOR i = ll_begin TO ll_end
//判断是否已存在
FOR j = 1 TO upper(ls_old[])
IF ls_old[j] = i THEN GOTO OVER;
NEXT
ls_temp += string(i,'……