Hello

I would like my program to be able to be registered but the code has to match or it won't register

I want the thing to be like

if Len(code) = 16 then
code = ucase(code)
DoCheckcode code
Else
MsgBox "invalid code", vbExclamation, "ERROR!"
end if

sub Docheckcode(code as String)
If left(code, 1) = A then
goto check2
else
goto badcode
end if

check2:
if left(code) = anynumber then
goto check3
else
goto badcode

check3:
if left(code) = B then
goto check4
else
goto badcode
end if
end sub

and so on

but where it says any number I want the program to see if its a number

my question is how can I make my program go to bad code if its a number greater then nine or not a number at all

I hope you can understand my question