/*
 * Program to test sort function: 
 * Generate a random sequence of N integers, sort them, and check
 * that the sort succeeded.  Program gets N from command-line 
 * argument.
 */
#include <stdio.h>
#include <stdlib.h>

/* counter for number of comparisons -- a bit ugly */
int num_compares = 0;

/* function declarations */
void fill_with_random(int nums[], int size);
void sort(int nums[], int size);
void sort_check(int nums[], int size);
int compare(const void *elem1, const void *elem2);

/* 
 * main program 
 */
int main(int argc, char* argv[]) {

	int N;
	int *nums;
    char *end_ptr; /* for strtol error checking */

    /* process command-line argument */
    if (argc < 2) {
        fprintf(stderr, "usage:  %s number_to_sort\n", argv[0]);
        return EXIT_FAILURE;
    }
    N = strtol(argv[1], &end_ptr, 10);
    if ((*end_ptr != '\0') || (N <= 0)) {
        fprintf(stderr, "number to sort must be a positive integer\n");
        return EXIT_FAILURE;
    }

    /* allocate space for array */
	nums = malloc(sizeof(*nums) * N);
	if (nums == NULL) {
		fprintf(stderr, "could not allocate space for %d ints\n", N);
		return EXIT_FAILURE;
	}

    /* fill, sort, check as before */
	fill_with_random(nums, N);
	sort(nums, N);
	sort_check(nums, N);

    /* print number of comparisons, collected during sort */
    fprintf(stdout, "%d comparisons\n", num_compares);

    /* free allocated space */
	free(nums);

	return EXIT_SUCCESS;
}

/* 
 * fills nums[0 .. size-1] with a random sequence of integers 
 */
void fill_with_random(int nums[], int size) {
	int i;
	for (i = 0; i < size; ++i) {
		nums[i] = rand();
	}
}

/* 
 * prints "sort succeeded" if nums[0 .. size-1] is in order,
 * "sort failed" if not 
 */
void sort_check(int nums[], int size) {
	int i;
	for (i = 0; i < size-1 ; ++i) {
		if ( !(nums[i] <= nums[i+1])) {
			printf("sort failed\n");
			return;
		}
	}
	printf("sort succeeded\n");
}


/*
 * sorts nums[0 .. size-1]
 */
void sort(int nums[], int size) { 
	qsort(nums, size, sizeof(nums[0]), &compare);
}

/*
 * compares two elements of the array (for qsort), also incrementing
 * global counter of number of comparisons
 */
int compare(const void *elem1, const void *elem2) {
	int *e1 = (int *) elem1;
	int *e2 = (int *) elem2;
    ++num_compares;
	if (*e1 < *e2)
		return -1;
	else if (*e1 > *e2)
		return 1;
	else
		return 0;
}