distance.c

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

    float distance(double, double, double, double);

    int main(void) 
    {
        //点P
        double latitude_s =  35.658581;   
        double longitude_s = 139.745433;
        //点Q
        double latitude_e = 43.062562;
        double longitude_e = 141.353650;

        double p2q = distance(latitude_s , longitude_s, latitude_e, longitude_e);
        printf("%f\n", p2q);
        return 0;
    }

    float distance(double latitude_s, double longitude_s, double latitude_e, double longitude_e)
    {
        double sin_lat_1 = sin(latitude_e * M_PI / 180);
        double cos_lat_1 = cos(latitude_e * M_PI / 180);
        double sin_lat_2 = sin(latitude_s * M_PI / 180);
        double cos_lat_2 = cos(latitude_s * M_PI / 180);
        double lamda1 = longitude_e * M_PI / 180;
        double lamda2 = longitude_s * M_PI / 180;
        double two_points_distance = 6370 * acos(sin_lat_1 * sin_lat_2 + cos_lat_1 * cos_lat_2 * 
        cos(lamda1 - lamda2));
        return two_points_distance;
    }