Calculate distance point from long/lat

fence_code.c

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

#define RAD(a) ((a) * (a) * M_PI)

double calculateDistance(double lat1, double lon1, double lat2, double lon2) {
    double R = 6371;
    double dLat = RAD(lat2-lat1);
    double dLon = RAD(lon2-lon1);
    double aX = sin(dLat/2) * sin(dLat/2) +
                cos(RAD(lat1)) * cos(RAD(lat2)) *
                sin(dLon/2) * sin(dLon/2);
    double c = 2 * atan2(sqrt(aX), sqrt(1 - aX));
    return R * c;
}

int main() {
  double startLat = 44.957;
  double startLong = -93.284;

  double endLat = 45.000;
  double endLong = -93.284;

  printf("TEST %f\r\n", calculateDistance(startLat, startLong, endLat, endLong));
  return 0;
}