Sort Struct

#include <stdio.h>
#include <stdlib.h>
typedef struct {
  double a;
  double b;
  double div;
} data_t;
int data_compare(const void *p1, const void *p2) {
  data_t *q1 = (data_t *) p1;
  data_t *q2 = (data_t *) p2;
  if (q1->div < q2->div) return 1;
  else if (q1->div > q2->div) return -1;
  else if (q1->a < q2->a) return -1;
  else if (q1->a > q2->a) return 1;
  else if (q1->b < q2->b) return -1;
  else if (q1->b > q2->b) return 1;
  return 0;
}
int main(void) {
  double a[] = { 2., 8., 4., 5., 10. };
  double b[] = { 3., 5., 4., 7., 10. };
  int n = sizeof(a) / sizeof(double);
  data_t dat[n];
  for (int i = 0; i < n; i++) {
    dat[i].a = a[i];
    dat[i].b = b[i];
    dat[i].div = a[i] / b[i];
  }
  for (int i = 0; i < n; i++) {
    printf("%2d %3.1lf %3.1lf %5.2lf\n", i + 1, dat[i].a, dat[i].b, dat[i].div);
  }
  puts("");
  qsort(dat, n, sizeof(data_t), data_compare);
  for (int i = 0; i < n; i++) {
    printf("%2d %3.1lf %3.1lf %5.2lf\n", i + 1, dat[i].a, dat[i].b, dat[i].div);
  }
  return EXIT_SUCCESS;
}