Calculate pi by using the formula pi/4 = 1/1 - 1/3 + 1/5 - 1/7 + 1/9 - ...

main.c

#include <stdio.h>
#include <stdlib.h>

double calc_pi(int terms) {
  double sum = 0;

  for (int n = 0; n <= 2 * terms; n++) {
    double term = 1.0 / (2 * n + 1);
    if (n % 2 == 0) {
      sum += term;
    }
    else {
      sum -= term;
    }
  }

  return 4 * sum;
}

int main(const int argc, const char** argv) {
  int terms = 1000;
  if (argc > 1) {
    terms = atoi(argv[1]);
  }

  printf("%lf\n", calc_pi(terms));

  return EXIT_SUCCESS;
}