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

/* BUG: returns pointer to local stack variable */
/* DO NOT do this in real code!                  */
int *bad_return(void)
{
    int local = 42;
    return &local;   /* dangling pointer — undefined behaviour */
}

/* CORRECT: allocate on heap so it outlives the function */
int *good_return(int value)
{
    int *p = malloc(sizeof(int));
    if (p) *p = value;
    return p;
}

/* CORRECT: caller provides storage */
void fill_values(int *out, int n)
{
    for (int i = 0; i < n; i++) out[i] = i * 10;
}

int main(void)
{
    /* Stack allocation — automatic lifetime */
    int  stack_arr[8];
    fill_values(stack_arr, 8);
    printf("Stack: %d %d %d
", stack_arr[0], stack_arr[1], stack_arr[2]);

/* Heap allocation — manual lifetime */
    int *heap_arr = malloc(8 * sizeof(int));
    if (!heap_arr) { perror("malloc"); return EXIT_FAILURE; }
    fill_values(heap_arr, 8);
    printf("Heap:  %d %d %d
", heap_arr[0], heap_arr[1], heap_arr[2]);
    free(heap_arr);

/* Heap scalar */
    int *hp = good_return(99);
    if (hp) {
        printf("Heap int: %d
", *hp);
        free(hp);
    }

printf("sizeof stack_arr: %zu bytes
", sizeof(stack_arr));
    return 0;
}