regarding this question for array append function in C using dynamic memory allocation

main.c

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

typedef struct intlist_ {
  int size;
  int* list;
} intlist;


void append(intlist* arr, int value){
  int* new_ptr = realloc((*arr).list, sizeof *((*arr).list) * ((*arr).size + 1u));
  if (new_ptr == NULL) {
    fprintf(stderr, "Output memory\n");
    exit (EXIT_FAILURE);
  }
  (*arr).list = new_ptr;
  (*arr).list[(*arr).size] = value;
  (*arr).size++;
}


int main() {

  intlist arr;
  arr.size = 4;
  arr.list = malloc(arr.size * sizeof(int));

  arr.list[0] = 0;
  arr.list[1] = 5;
  arr.list[2] = 3;
  arr.list[3] = 64;

  // for (int ii = 0; ii < arr.size; ii++)
    // printf("%d, ", arr.list[ii]);

  append(&arr, 12);

  for (int ii = 0; ii < arr.size; ii++)
    printf("%d, ", arr.list[ii]);

  free(arr.list);
  return 0;
}

regarding this question.