John, for folk/traditional whistlers (are there any others?) you'd be better transposing everything to D, which is the "home" whistle for most. Few would be comfortable sight-reading music in C.

I wonder if you had already made the mental transposition to D when you were asking how to finger C/c sharp. This is how Alison has read it, and has given you the fingering as it is on a D whistle. On a C whistle you would get it by covering five and a half holes.