Confusion regarding scale direction

Using “Wish you were here” as an example. The first 3 notes, C B G have an up sign before C. So am I going up 11 semi-tones to B and then up 8 more to G? Or does it mean that any note without an up sign goes down. C 1 semi-tone to B, B four semi-tones to G?

I want to experiment with chromatic inversions of melodies and this will be a great tool once I understand it.

Thank you in advance for your help.