Найти центр и радиус окружности

#include <stdbool.h>
#include <math.h>
#include <stdio.h>
 
#define SWAP(T, a, b) do { T tmp = (a); (a) = (b); (b) = tmp; } while (0)
#define ROL3(T, a) do { T tmp = (a)[0]; (a)[0] = (a)[1]; (a)[1] = (a)[2]; (a)[2] = tmp; } while (0)
#define MIN(a, b) ((a) < (b) ? (a) : (b))
 
typedef struct pnt_t { int x, y; } pnt_t;
 
pnt_t ccw_90(pnt_t p) 
  { return (pnt_t) { -p.y, p.x }; }
 
pnt_t minus(pnt_t a, pnt_t b)
  { return (pnt_t) { a.x - b.x, a.y - b.y }; }
  
double length(pnt_t p)
  { return hypot(p.x, p.y); }
  
int product(pnt_t a, pnt_t b)
  { return a.x * b.x + a.y * b.y; }
 
int side(pnt_t a, pnt_t b, pnt_t p)
{
  int cp = product(ccw_90(minus(b, a)), minus(p, a));
  return (cp > 0) - (cp < 0);
}
 
void make_ccw(pnt_t (*t)[3])
{
  if (side((*t)[0], (*t)[1], (*t)[2]) < 0)
    SWAP(pnt_t, (*t)[0], (*t)[1]);
}
 
double angle_measure(pnt_t a, pnt_t o, pnt_t b)
{
  a = minus(a, o);
  b = minus(b, o);
  return -product(a, b) / (length(a) * length(b));
}
 
double min4(double a, double b, double c, double d)
{
  double ab = MIN(a, b), cd = MIN(c, d);
  return MIN(ab, cd);
}
 
bool test_inside(pnt_t (*t)[3], pnt_t p)
{
  make_ccw(t);
 
  int s[] = { side((*t)[0], (*t)[1], p), side((*t)[1], (*t)[2], p), side((*t)[2], (*t)[0], p) };
  
  unsigned outside = (s[0] < 0) + (s[1] < 0) + (s[2] < 0);
  if (outside != 1)
    return outside == 0;
 
  while (s[0] >= 0)
  {
    ROL3(pnt_t, *t);
    ROL3(int, s);
  }
  
  double 
    min_org = min4(
      angle_measure((*t)[0], (*t)[1], (*t)[2]), angle_measure((*t)[2], (*t)[0], (*t)[1]), 
      angle_measure((*t)[1], (*t)[0], p), angle_measure(p, (*t)[1], (*t)[0])),
    min_alt = min4(
      angle_measure((*t)[1], (*t)[2], p), angle_measure(p, (*t)[2], (*t)[0]), 
      angle_measure((*t)[0], p, (*t)[2]), angle_measure((*t)[2], p, (*t)[1]));
    
  return min_org <= min_alt;
}
 
int main()
{
  printf("%s\n", 
    test_inside(&(pnt_t []) { { 5, 5 }, { 15, 2 }, { 12, 8 } }, (pnt_t) { 8, 10 }) ? "Inside" : "Outside");
  printf("%s\n", 
    test_inside(&(pnt_t []) { { 5, 5 }, { 15, 2 }, { 12, 8 } }, (pnt_t) { 8, 8 }) ? "Inside" : "Outside");
  printf("%s\n", 
    test_inside(&(pnt_t []) { { 5, 5 }, { 15, 2 }, { 12, 8 } }, (pnt_t) { 12, 5 }) ? "Inside" : "Outside");
  printf("%s\n", 
    test_inside(&(pnt_t []) { { 5, 5 }, { 15, 2 }, { 12, 8 } }, (pnt_t) { 18, 0 }) ? "Inside" : "Outside");
}