VBA or Validation?
 

Hi, I have a couple of things I am trying to do, for whatever row of data
entered:

if A# is not blank, then I want the user must select a value from the list
and/or must type in only a value that is in this list
AND
if A# is not blank, then I want the user must not leave cells in C# blank,
but can enter any text up to 200 characters
AND
if A# is not blank, then I want the user must not leave cells in C# blank,
but can enter any value between 0-100%

I already have the cells set up with validation drop down lists. If it is
not possible to do the following within the validation function, I'd like to
get some VBA script that would trigger the errors upon save, and not allow
them to save the document until all the errors were fixed.