#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <gsl/gsl_rng.h>

int main(int argc, char** argv){
  size_t size = atoi(argv[1]);             // size of the generated sample

  // Initialize an RNG.
  gsl_rng_env_setup();
  gsl_rng *r = gsl_rng_alloc(gsl_rng_default);

  // Random points (x, y) generation: x in [0,1), y in [0,3)
  // get if   y < exp(x)
  // leave if y > exp(x)
  size_t in = 0;
  size_t total = 0;
  do{
    double x = gsl_rng_uniform(r);
    double y = 3 * gsl_rng_uniform(r);
    if (y <= exp(x)){
      in++;
    }
    total++;
  } while (total < size);

  
  // The integral is esitmated thorugh the proportion:
  // integral : 3 = in : total
  double integral = 3.0*(double)in/(double)total;
  printf("∫exp(x)dx in [0,1]:\t%.07f\n", integral);

  // Free memory
  gsl_rng_free(r);
  return EXIT_SUCCESS;
}