How to use dynamically allocated arrays

main.c

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

int* arr;
size_t arrSize = 256;

// 1) Do you need an array used in many other places?
// 2) Do you know the max amount of elements?
// 3) Is that max amount too big?
int main(int argc, char* argv[]) {
    arr = calloc(256, sizeof(int));
    if (arr == NULL) {
        fprintf(stderr, "Array not allocated!\n");
        return 1;
    }
    
    arr[10] = 17;
    printf("%d\n", arr[10]);
    
    arrSize *= 2;
    arr = realloc(arr, arrSize * sizeof(int));
    if (arr == NULL) {
        fprintf(stderr, "Array not reallocated!\n");
        return 1;
    }
    printf("%d\n", arr[10]);
    
    free(arr);
    return 0;
}