/**
 * Program to test sorting function:
 *
 * Generate array of N random values.
 *
 * Sort the array, counting comparisons.  
 *
 * Check that the result is sorted.
 *
 * Input:  Number of elements.
 *
 * Output:  Whether sort worked, and the numbers of comparisons.
 */
#include <stdio.h>
#include <stdlib.h>

/* ---- Function declarations ---- */
/* Note use of C99 variable-length arrays as parameters (where
 * appropriate)
 */

void test_and_print(int n);
void generate_data(int n, int nums[n]);
int find_index_of_max(int nums[], int last, int *num_compares);
void selection_sort(int n, int nums[n], int *num_compares);
void is_sorted(int n, int nums[n]);

/* ---- Main program ---- */

int main(void) {
	int n;
	printf("how many numbers?\n");
	if ((scanf("%d", &n) != 1) || (n <= 0)) {
		printf("input not a positive number\n");
		return EXIT_FAILURE;
	}
	test_and_print(n);
	return EXIT_SUCCESS;
}

/* ---- Function definitions ---- */

/*
 * Generate data (n elements), sort, check, and print results, as described
 */
void test_and_print(int n) {
	int nums[n];
	int num_compares = 0;
	generate_data(n, nums);
	selection_sort(n, nums, &num_compares);
	printf("is it sorted?  (no news is good news)\n");
	is_sorted(n, nums);
	printf("number of comparisons:  %d\n", num_compares);
}

/* 
 * Generate n elements and put in nums 
 */
void generate_data(int n, int nums[n]) {
	int i;
	for (i = 0; i < n; ++i) {
		nums[i] = rand();
	}
}

/*
 * Find largest element in nums[0 .. last] and return its index.
 * (Also modify *num_compares.)
 */
int find_index_of_max(int nums[], int last, int *num_compares) {
	int max;	/* index of maximum so far */
	int i;
	max = 0;
	for (i = 1; i <=last; ++i) {
		if (nums[i] > nums[max])
			max = i;
		*num_compares += 1;
	}
	return max;
}

/* 
 * Sort nums (array of size n).
 */
void selection_sort(int n, int nums[n], int *num_compares) {

	int last;
	int index_of_max;
	int temp;

	for (last = n-1; last > 0; --last) {
		index_of_max = find_index_of_max(nums, last, num_compares);
		/* exchange nums[index_of_max] and nums[last] */
		temp = nums[index_of_max];
		nums[index_of_max] = nums[last];
		nums[last] = temp;
	}
}

/* 
 * Check that nums (array of size n) is sorted.
 * Prints messages about anything not sorted.
 */
void is_sorted(int n, int nums[n]) {
	int i = 0;
	for (i = 0; i < n-1; ++i) {
		if (nums[i] > nums[i+1])
			printf("out of order at %d!\n",i);
	}
}