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

double f(double x) {
   double return_val;

   return_val = x*sin(10*x);
   return return_val;
}

double Trap(double a, double b, int n) {
   double integral;
   int   i;
   double h;

   h = (b-a)/n;
   integral = 0.5 * ( f(a)+f(b) );
   for(i=1; i<=n-1; i++) {
      integral += f(a+i*h);
   }
   integral *= h;
   return integral;
}

int main() {
   double a = 0.0;
   double b = 12.0;
   int    n = 100000000;
   double result;
    
   result = Trap(a,b,n);
   printf("\nThe calculated result is %f.\n", result);
}