GREP style for three digit code NOT followed by specific characters

Question

I'm trying to set up a GREP style that will style a 3 digit code (example 789) but not apply that style when the code is followed by the characters ct.

So the style would apply to the 100 in "100 Halo" but not to the 120 in "120 ct"

Answer 1

This is the GREP:

\d{3}(?!\sct)

All the numbers \d repeated three times {3} (excepting those ?! followed by a space \s and the characters ct )