point arr

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#define STEP (1 << 8)

void allocCheck(void *p) {
  if (!p) {
    perror("");
    exit(EXIT_FAILURE);
  }
}

typedef struct {
  int x, y;
} Point;

typedef struct {
  int len, buff;
  Point *at;
} DynArr;

int readPoint(Point *p, FILE *file) {
  char aux;
  int read = fscanf(file, "%d%c%d", &(p->x), &aux, &(p->y));
  return read == 3 && aux == '.';
}

DynArr *mkArr(int ini) {
  DynArr *arr = malloc(sizeof(DynArr));
  allocCheck(arr);
  arr->len = arr->buff = ini;
  if (ini) {
    arr->at = calloc(sizeof(Point), ini);
    allocCheck(arr->at);
  } else {
    arr->at = NULL;
  }
  return arr;
}

void add(Point p, DynArr *arr) {
  if (arr->len == arr->buff) {
    arr->buff += STEP;
    arr->at = realloc(arr->at, sizeof(Point) * arr->buff);
    allocCheck(arr->at);
  }
  arr->at[(arr->len)++] = p;
}

void printPoint(const Point *const point, FILE *file) {
  fprintf(file, "{ x:%d y:%d }\n", point->x, point->y);
}

void printArr(const DynArr *const arr, FILE *file) {
  for (int i = 0; i < arr->len; i++) {
    printPoint(&(arr->at[i]), file);
  }
}

int getMag(const Point *const p) {
  int x = p->x, y = p->y;
  return x * x + y * y;
}

Point getClosest(const DynArr *const arr) {
  int minMag = INT_MAX;
  Point res = {};
  for (int i = 0; i < arr->len; i++) {
    int newMag = getMag(&(arr->at[i]));
    if (minMag > newMag) {
      minMag = newMag;
      res = arr->at[i];
    }
  }
  return res;
}

int main(void) {
  DynArr *arr = mkArr(0);
  for (Point p; readPoint(&p, stdin);) {
    add(p, arr);
  }

  printArr(arr, stdout);
  printf("closest to O: ");
  Point res = getClosest(arr);
  printPoint(&res, stdout);//*/
  free(arr->at);
  free(arr);
  return 0;
}