vba - How can I check if a string only contains letters? -

i'm using function allows me review string of text , evaluate if composed of letters. housed in module called "general". general module exists house public functions , variables. function code listed below:

public function isalpha(strvalue string) boolean dim intpos integer      intpos = 1 len(strvalue)         select case asc(mid(strvalue, intpos, 1))             case 65 90, 97 122                 isletter = true             case else                 isletter = false                 exit         end select     next end function   

next have 2 "if" routines evaluate first 2 characters of textbox in userform. first routine asks if 1st character numeric , second routine asks if 2nd character alpha. currently, second "if" routine ejecting me sub-routine when isalpha tests true, rather generating msgbox. isalpha function not being called correctly?

if routines code listed below:

private sub cmdmap_click()      txtdxcode         if isnumeric(left(me.txtdxcode.text, 1))             msgbox "incorrect dx code format entered. ", vbexclamation, "dx code entry"             txtdxcode.value = ""             txtdxcode.setfocus             exit sub         end if          if isalpha(left(me.txtdxcode.text, 2))             msgbox "incorrect dx code format entered. ", vbexclamation, "dx code entry"             txtdxcode.value = ""             txtdxcode.setfocus             exit sub         end if     end 

why don't use regular expressions instead? there's no loops involved:

public function isalpha(strvalue string) boolean     isalpha = strvalue worksheetfunction.rept("[a-za-z]", len(strvalue)) end function 

also, when create user-defined function (udf) need ensure return value assigned name of actual function, in case isalpha - not isletter otherwise value never passed back.