#include <math.h>

double simpson(double x0, double x1, int n2)
{
	double dx = (x1 - x0) / n2;

	int i;
	double sum = 0;
	for (i = 0; i <= (n2/2)-1; i++)
	{
		sum += sin(x0 + 2*i*dx) + 2*sin(x0 + (2*i + 1)*dx);
	}

	return (dx/3) * (sin(x1) - sin(x0) + 2*sum);
}