an example to use iterator instead of ugly fuck i. See also https://crypto.stanford.edu/~blynn/c/cruft.html

iter.c

#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>

#define REP(x, n) for (int x = 0; x < n; x++)
#define REP1(x, n) for (int x = 1; x <= n; x++)
#define NELEM(a) (sizeof(a)/sizeof(a[0]))

struct test_t {
  int * arr;
  size_t size;
};

struct test_t new_test(size_t n) {
  int * p = malloc(n * sizeof(int));
  /* a better way to restrict local variable if you really wanted to */
  /* https://stackoverflow.com/questions/2687392/is-it-possible-to-declare-two-variables-of-different-types-in-a-for-loop */
  for (struct {int idx; int * it; } s = { 0, p }; s.it < p + n; s.idx++, s.it++) {
    *s.it = s.idx;
  }
  struct test_t t = (struct test_t) {
    .arr = p,
    .size = n
  };
  return t;
}

static inline int * test_begin(struct test_t *t){
    return t->arr;
}

static inline int * test_end(struct test_t *t){
    return t->arr + t->size;
}

int main() {
  struct test_t arr[3] = {
    new_test(3),
    new_test(10),
    new_test(2)
  };

  for (struct {int idx; struct test_t * it;} s = {0, arr}; s.it < arr + NELEM(arr); s.idx++, s.it++) {
    printf("idx: %d, size: %d\n", s.idx, (int) s.it -> size);
    for (struct { int at; int * it; } i = {0, test_begin(s.it)}; i.it < test_end(s.it); i.at++, i.it++) {
      printf("idx: %d, value at %d is %d\n", s.idx, i.at, *i.it);
    }
  }

  return 0;
}