2 they count C-Class?
 

hey guys, its very urgent...
2 the flight attendants at SQ count how many people are in the C and F class?

Don't know. But I know they have a list of names of the F and C Class pax as they supposed to address them by names. So they will know who is missing or who is not.

They know which seat should be empty or occupied.

If the seat is occupied, they know the name of the passenger in that seat.

If the seat is supposed to be empty and a passenger sits in that seat, they causally ask for the boarding pass just for clarification.

I was on a IST-DXB flight once where a Y passenger decided to "upgrade" himself to a empty C class seat ... he was given assistance to the correct seat number on his boarding pass.

No, they don't count, they check it seat by seat. :p Once I moved to another seat as there were two seats open on that row; a FA came over with a manifest to check and marked it. :)

As they normally address each seat's occupant by their names, I don't know how they wouldn't know the number of F/C pax.