// Integration function using function object
#include <iostream>
#include <cmath>
using namespace std;

class Integrand
{
public:
  double operator()(double &x) {return pow(sin(x),3);}
};
double integrate(Integrand,const double &,const double &);
int main()
{              
  double res,a=1.0,b=2.0;
  Integrand fun;
  res = integrate(fun,a,b);
  cout<<"integral = "<<res<<endl; 
}    

double integrate(Integrand f,const double &a,const double &b){
  // rough Riemann sum integration
  const int N=1000000;
  double res = 0, x = a;
  double dx = (b-a)/(N-1);
  for (int i=0; i<N; i++) {
     res += f(x);
     x   += dx;  
  }
  return dx*res;
}