#include<stdio.h>
#include<math.h>

double f1(double x){
  double r=1.0;
  double return_val;
  double arg = r*r-x*x;
  if (arg<0.) arg=0.;
  return_val = sqrt(arg);
  return return_val;
}


double f2(double x){
  return x*sin(10*x);
}


double trapez(double a, double b, int n){
  int i;
  double sum=0.;
  double h=(b-a)/(float)n;
  double xa=a;
  double xb=a+h;

  for (i=0; i<n; i++){
    sum += (f2(xa)+f2(xb))/2. * h;
    xa = xb;
    xb += h;
  }
  return sum;
}


void main(int argc, char **argv){

  double gesamt;
  double a,b;
  int n_ges;

  n_ges=400000000;
  a = 0.;
  b = 2*3.141592654;

  gesamt = trapez(a,b,n_ges);
  printf("gesamt = %f\n",gesamt);

}