#include <stdio.h>
#include <stdbool.h>
#include <assert.h>
#include <math.h>
#include <values.h>

double mean(double set[], int set_n) {
  double sum = 0.0;
  for (int i=0; i<set_n; i++) {
    sum += set[i];
  }

  return sum/set_n;
}

bool isalmost(double x, double c, double epsilon) {
  assert(epsilon >= 0.0);
  return fabs(x-c) < epsilon;
}

double sample_variance(double set[], int set_n) {
  double m = mean(set, set_n);

  double ss = 0.0;
  for (int i=0; i<set_n; i++) {
    ss += pow((set[i]-m), 2.0);
  }

  // Divide by (n-1), as this is *sample* variance (Bessel's correction).
  assert(set_n>1);
  ss /= (set_n-1);

  return ss;
}

double sample_stddev(double set[], int set_n) {
  return sqrt(sample_variance(set, set_n));
}

double set_min(double set[], int set_n) {
  double min = MAXDOUBLE;

  for (int i=0; i<set_n; i++) {
    min=fmin(set[i], min);
  }

  return min;
}

double set_max(double set[], int set_n) {
  double max = MINDOUBLE;

  for (int i=0; i<set_n; i++) {
    max=fmax(set[i], max);
  }

  return max;
}

double range(double set[], int set_n) {
  return set_max(set, set_n) - set_min(set, set_n);
}

int main() {
  // Some data
  double d[] = {7, 8, 5, 1, 6, 2};
  const int d_n = 6;

  double e[] = {-10, 0, 10, 11, 12, 13, 14, 8, 9, 10, 11, 10, 10};
  const int e_n = 13;

  // Some tests
  assert(isalmost(mean(d, d_n), 4.833, 0.001));
  assert(isalmost(mean(e, e_n), 8.307, 0.001));

  // XXX assert(isalmost(median(d, d_n), 5.5, 0.001));
  // XXX assert(isalmost(median(e, e_n), XXX, 0.001));

  assert(isalmost(sample_variance(d, d_n),  7.766, 0.001));
  assert(isalmost(sample_variance(e, e_n), 41.564, 0.001));

  assert(isalmost(sample_stddev(d, d_n), 2.787, 0.001));
  assert(isalmost(sample_stddev(e, e_n), 6.447, 0.001));

  assert(isalmost(set_min(d, d_n),   1.0, 0.001));
  assert(isalmost(set_max(d, d_n),   8.0, 0.001));
  assert(isalmost(set_min(e, e_n), -10.0, 0.001));
  assert(isalmost(set_max(e, e_n), +14.0, 0.001));

  assert(isalmost(range(d, d_n),  7.0, 0.001));
  assert(isalmost(range(e, e_n), 24.0, 0.001));

  // XXX Mode
  // XXX Percentile
}