C++ Code for an iterative sum

typedef double valuetype; // you didn't tell us the type for val ;-)

class sequencer {
public:
   virtual valuetype getNext(valuetype v) = 0; //prototype for the iteration function
   valuetype getAt(std::size_t iterations, valuetype initial_value) {
      v = initial_value;
      for (std::size_t i = 0; i < iterations; ++i) {
          v = getNext(v);
      }
      return v;
   }
};

class AddSinusSequence : public sequencer {
public:
   virtual valuetype getNext(valuetype v) {
      return v + sin(v);
   }
};

int main() {
   AddSinusSequence ass;
   std::cout << "first value: " << 1.5 << std::endl;
   std::cout << "fifth value: " << ass.getAt(5, 1.5) << std::endl;
   return 0;
}

double AddSinus(double value) {
   return value + sin(value);
}
double getAt(unsigned i, double initial_value) {
   double v = initial_value;
   for (unsigned i=0; i < iterations; ++i)
      v = AddSinus(v);
   return v;
}
int main() {
   double initial = 1.5;
   double v_at_5 = getAt(5, initial);
   // output as needed ...
   return 0;
}