Sort by BMI

#include <stdio.h>
#include <stdlib.h>
typedef struct {
  char name[64];
  double height;
  double weight;
} person;

double bmi(person p) {
  double a = p.height / 100;
  return p.weight / (a * a);
}

void swap(person *p1, person *p2) {
  person p = *p1;
  *p1 = *p2;
  *p2 = p;
}

void sort_by_bmi(person *p, int n) {
  int k = n;
  while (k >= 0) {
    int j = -1;
    for (int i = 1; i <= k; i++) {
      if (bmi(p[i - 1]) > bmi(p[i])) {
        j = i - 1;
        swap(&p[j], &p[i]);
      }
    }
    k = j;
  }
}

int main(void) {
  person p[] = {
    { "一郎", 180.3, 77.1 },
    { "二郎", 188.0, 93.0 },
    { "三郎", 170.0, 63.0 },
    { "四郎", 171.8, 59.0 },
    { "五郎", 168.1, 56.5 },
    { "六郎", 173.7, 69.4 },
    { "七郎", 178.5, 60.3 },
    { "八郎", 175.2, 70.9 },
    { "九郎", 169.6, 55.7 },
  };
  sort_by_bmi(p, sizeof(p) / sizeof(person));
  for (int i = 0; i < sizeof(p) / sizeof(person); i++) {
    printf("%i: %s (%.1f)\n", i, p[i].name, bmi(p[i]));
  }
  return EXIT_SUCCESS;
}