Make room for a variable-sized count

The desk chooses how many counts to store when the program runs. malloc requests enough bytes for them and returns a pointer, or NULL on failure. The expression sizeof *counts measures one element without repeating its type. Because the allocated elements start without usable values, check the pointer first and initialize every element before reading it. Release the allocation with free after the last use.

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

int main(void) {
    size_t n = 3;
    int *counts = malloc(n * sizeof *counts);
    if (counts == NULL) {
        fprintf(stderr, "Allocation failed\n");
        return 1;
    }
    for (size_t i = 0; i < n; i++) {
        counts[i] = (int) (i + 1);
    }
    printf("Total: %d\n", counts[0] + counts[1] + counts[2]);
    free(counts);
    counts = NULL;
    return 0;
}

No array element is read before it has a value. counts = NULL protects this particular variable against accidental reuse, but it cannot repair other copies of the freed address. For the exercise, repeat that order with different counts: allocate, check, fill, read, free.