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

double approximate_pi(unsigned int steps) {
  double approximate_pi = 4.0;
  bool subtract = true;

  /* Gregory–Leibniz series */
  for (unsigned int i = 2; i <= steps; i++) {
    if (subtract) {
      approximate_pi -= (4.0 / (i * 2 - 1));
    } else {
      approximate_pi += (4.0 / (i * 2 - 1));
    }
    subtract = !subtract;
  }

  return approximate_pi;
}

int main(void) {
  // printf("sizeof(int) = %d\n", sizeof(int));

  double mypi = approximate_pi(100000000);

  printf("pi = %8.7f\n", mypi);
  assert(mypi > 3.141);
  assert(mypi < 3.142);

  return 0;
}