What is the complexity classification of sat(..) ?

 typedef unsigned int UInt;
 typedef bool (*Func)(UInt);

 // [Ret] true, if ∃c, 0<=c<=n, f(c)==1 and f is a P-time function.
 //       false, otherwise.
 //
 bool sat(Func f, UInt n) {
   for(Uint c=0; c<=n; ++c) {
     if(f(c)) return true;
   }
   return false;
 }

 Q: If it is NPC, what is the proof? If it it not, what is the complexity
    classification of sat(..)?