How do you calculate speed by Longitaude and latitude in c p

How do you calculate speed by Longitaude and latitude in c programming with an array with forward difference method

Solution

#include<math.h>

#define pi 3.14159265358979323846

/*Function prototypes*/

double deg2rad(double);

double rad2deg(double);

double distance(double lat1, double lon1, double lat2, double lon2, char unit)

{

double theta, dist;

theta=lon1-lon2;

dist=sin(deg2rad(lat1) * sin(deg2rad(lat2)) + cos(deg2rad(lat1)) * cos(deg2rad(lat2)) * cos(deg2rad(theta));

dist=acos(dist);

dist=rad2deg(dist);

dist=dist * 60 * 1.1515;

switch(unit)

{

case \'M\':

break;

case \'K\':

dist=dist * 1.609344;

break;

case \'N\':

dist=dist * 0.8684;
break;

}

return (dist);

}

/* This function converts decimal degrees to radians */

double deg2rad(double deg)

{

return (rad * 180/pi);

}