/* Implementation of the simple 'array' ADT, plus a short main program
   for testing.
*/

#include "anx15-02.h"
#include <stdlib.h>
#include <stdio.h>

/**** array_create ****
 On entry: size is the number of elements needed in the array.
 On exit:  returns a pointer to an array, or NULL.
*/
ARRAY * array_create(int size) {
    ARRAY * A;
    A = (ARRAY*) malloc(sizeof(ARRAY));
    if (A == NULL) {
        return NULL;                                    /* failure */
    }
    A->elements = (float*)malloc(size * sizeof(float)); /* Allocate elements */
    if (A->elements == NULL) {
        free(A);
        return NULL;
    }
    A->size = size;
    return A;
}

/**** array_free ****
 On entry: arr is a pointer to an array.
 On exit:  The array has been freed.
*/
void array_free(ARRAY * arr) {
    free(arr->elements);    /* MUST free in this order! (Do you see why?) */
    free(arr);
}

/* static */ void check_bounds (ARRAY * a, int n);

/**** array ****
 On entry: arr is an ARRAY, n is the index of the required element.
 On exit:  Returns the value of the selected element.
*/
float array(ARRAY * arr, int n) {
    check_bounds(arr, n);
    return arr->elements[n];
}

/**** array_set ****
 On entry: arr is an ARRAY, n is the index of an element.
 On exit:  Element n of arr has been assigned the value f.
*/
void array_set(ARRAY * arr, int n, float f) {
    check_bounds(arr, n);
    arr->elements[n] = f;
}

/* check-bounds: Does nothing if the index is within the array, else
   prints an informative message, and terminates the program.

   Note: If you have read section 18.3, this function should be static.
*/

/* static */ void check_bounds (ARRAY * a, int n) {
    if (n < 0 || n >= a->size) {
        fprintf(
            stderr, "ERROR: Request for element %d in a %d-element array\n",
            n, a->size
        );
        exit(1);
    }
}

/************************************************************************
    Test main program.  Allocates a 10-element array, fills each element
    with its own index+.5, then tries to print 11 elements.  Should end
    with an error!
*/

main () {
    ARRAY * ap;
    int i;
    ap = array_create(10);
    if (ap == NULL) {
        fprintf(stderr, "Cannot allocate the array.\n");
        exit(1);
    }
    printf("Setting the array elements:\n");
    for (i=0; i<10; i++) {
        array_set(ap, i, i + 0.5);
        printf("ap[%d] set to %f\n", i, i + 0.5);
    }
    printf(
        "Checking the elements; we try to check element 11, so we\n"
        "should end with an error message.\n"
    );
    for (i=0; i<11; i++) {
        array_set(ap, i, i + 0.5);
        printf("ap[%d] is %f\n", i, array(ap,i));
    }
    printf("You should never read this!!\n");
    exit(0);
}