search array for dupes add item if not found

[Gjbth]

Thank you for that Gintaras, that reply was almost immediate.

If I may ask for a little more advice.

In my proposed macro. I have created an array from my text file and named the array a1.
I will assign the array to a combobox with :

ARRAY(str) a1=cb3Sit
a1.sort(2)
cb3Sit=a1

using your function how would I call it to check the entered value in cb3Sit against a1 then write a1 back to a file.

Please forgive me if this is simple, I am still learning