Challenge 1: Allocating, Filling, Printing, and Freeing an int Array — Possible Solution
====================================================================

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

int main() {
    int *nums = malloc(5 * sizeof(int));
    if (nums == NULL) {
        return 1;  // allocation failed
    }

    for (int i = 0; i < 5; i++) {
        nums[i] = i + 1;
    }

    for (int i = 0; i < 5; i++) {
        printf("%d\n", nums[i]);
    }

    free(nums);
    return 0;
}

Output:

    1
    2
    3
    4
    5

WHY THIS WORKS AS AN ANSWER
------------------------------
The NULL check happens immediately after malloc, before the memory is
ever used -- per the chapter, malloc's failure return must always be
checked, not assumed away. The array is filled and printed while nums
is still a valid pointer, and free(nums) is the last thing that
happens, only after every use of the memory is complete.