Managing an array containing structure pointers

/* structlist.c
 * A testing program for managing an array containing structure pointers. */

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

#define MAX_STRUCT_COUNT 5
#define MAX_ITERATION_COUNT 10

typedef struct {
    int x;
    int y;
    int index;
} test_struct_t;

test_struct_t* struct_list[MAX_STRUCT_COUNT];

test_struct_t* add_struct(int x, int y) {
    // find the next free position in the array

    for (int i = 0; i < MAX_STRUCT_COUNT; i++) {
        if (struct_list[i] == NULL) {
            if ((struct_list[i] = malloc(sizeof(test_struct_t))) == NULL) {
                return NULL;
            }

            struct_list[i]->x = x;
            struct_list[i]->y = y;
            struct_list[i]->index = i;

            return struct_list[i];
        }
    }

    return NULL;
}

void remove_struct(test_struct_t* target) {
    struct_list[target->index] = NULL;
    free(target);
}

int main(void) {
    int valid_structs = 0;
    int max_iterations = (MAX_ITERATION_COUNT > 255) ? 255 : MAX_ITERATION_COUNT;

    // register structs

    for (int i = 0; i < max_iterations && valid_structs < MAX_STRUCT_COUNT; i++) {
        printf("Iteration %d: ", i + 1);

        if (!add_struct(i, i + 4)) {
            printf("Could not create struct; skipping...\n");
            struct_list[i] = NULL;
            continue;
        }

        printf("Created struct at pos. %d with X = %d and Y = %d\n", struct_list[valid_structs]->index, struct_list[valid_structs]->x, struct_list[valid_structs]->y);
        valid_structs++;
    }

    if (valid_structs < 1) {
        fprintf(stderr, "No structs could be created... exiting\n");
        return 1;
    }

    // testing (free a random one)

    printf("\nSuccessfully created %d structs (max iteration count of %d).\n\nFreeing a random one...\n", valid_structs, max_iterations);

    srand(time(NULL));
    int target;
    while (struct_list[target = rand() % MAX_STRUCT_COUNT] == NULL);

    printf("Removing struct at pos. %d: %p (x = %d, y = %d)\n", target, struct_list[target], struct_list[target]->x, struct_list[target]->y);
    remove_struct(struct_list[target]);
    printf("Removed struct at pos. %d\nProof: struct_list[%d] = %p\n", target, target, struct_list[target]);

    // auto-cleanup

    for (int i = 0; i < MAX_STRUCT_COUNT; i++) {
        if (struct_list[i] != NULL) {
            remove_struct(struct_list[i]);
        }
    }

    printf("\nAll other structs cleaned.\nExiting...\n\n");

    return 0;
}