Thread: wad wrong with this code?

Code:

#include <stdio.h>
#include <math.h>
#define PI 3.141593

//// macro (used in earlier tutorial), suitable for one liner function
#define deg_to_rad(deg) (deg * (PI/180.0))

//// function prototypes
double angle(double x1, double y1, double z1, double x2, double y2, double z2);

//// prototype of function to find the great circle distance between two points
double gc_dist(double, double, double, double);

int main(void) {
  double lat1, long1, lat2, long2;
  
  printf("Enter latitude north and longitude west ");
  printf("for location 1 : ");
  scanf("%lf %lf", &lat1, &long1);

  printf("Enter latitude north and longitude west ");
  printf("for location 2 : ");
  scanf("%lf %lf", &lat2, &long2);
  printf("Great Circle Distance: %.0f km\n", gc_dist(lat1, long1, lat2, long2));
}

double angle(double x1, double y1, double z1, double x2, double y2, double z2) {
  double dot, dist1, dist2;
 
  dot = x1 * x2 + y1 * y2 + z1 * z2; // find the dot product of the two vectors
  dist1 = sqrt(x1 * x1 + y1 * y1 + z1 * z1); // find length of each vector
  dist2 = sqrt(x2 * x2 + y2 * y2 + z2 * z2);

  return acos(dot / (dist1 * dist2));
}
	double gc_dist(double lat1, double long1, double lat2, double long2) {
  double rho = 6371, phi, theta, gamma, dot, dist1, dist2, x1,y1,z1,x2,y2,z2;

  phi = deg_to_rad(90 - lat1); // convert to spherical coordinates
  theta = deg_to_rad(360 - long1);
  x1 = rho * sin(phi) * cos(theta); // find rectangular coordinates for p1
  y1 = rho * sin(phi) * sin(theta);
  z1 = rho * cos(phi);
  phi = deg_to_rad(90 - lat2); // repeat for p2
  theta = deg_to_rad(360 - long2);
  x2 = rho * sin(phi) * cos(theta);
  y2 = rho * sin(phi) * sin(theta);
  z2 = rho * cos(phi);
  return angle(x1, y1, z1, x2, y2, z2) * rho;
}

given
Enter latitude north and longitude west for location 1 : 36.12 86.67
Enter latitude north and longitude west for location 2 : 33.94 118.40
Great Circle Distance: 2886 km

but i got 3497km...

did i specify the wrong macro ?
or i return the wrong value ?

Code:

double angle(double x1, double y1, double z1, double x2, double y2, double z2) {
  double dot, dist1, dist2;
 
  dot = (x1 * x2) + (y1 * y2) + (z1 * z2); // find the dot product of the two vectors
  dist1 = sqrt((x1 * x1) + (y1 * y1) + (z1 * z1)); // find length of each vector
  dist2 = sqrt((x2 * x2) + (y2 * y2) + (z2 * z2));
}

solved .. deg_to_rad((x-y));
eg. phi=deg_to_rad((90 - lat1));

double brackets are needed for the math arithemtic to work
so if any students are doing this question as well... this is the answer for you guys =)..