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

/*
 * This program demonstrates using qsort with different comparison
 * functions.
 */

/*
 * This function compares two integers for sorting ascending.
 */
int intasc(const void *a, const void *b)
{
	return *(int *)a - *(int *)b;
}

/*
 * This function compares two integers for sorting ascending.
 */
int intdesc(const void *a, const void *b)
{
	return *(int *)b - *(int *)a;
}

/*
 * This sorts the intgers so that the odd ones come first, and otherwise
 * ascending.
 */
int intoddeven(const void *_a, const void *_b)
{
	int a = *(int *)_a;
	int b = *(int *)_b;

	if((a & 1) && !(b & 1)) return -1; /* a is odd, b is even.  a first */
	if(!(a & 1) && (b & 1)) return 1; /* b is odd, a is even.  b first */
	return a - b;
}

/*
 * This one compares strings to sort descending.  The array being sorted 
 * will be an array of pointers to char.  The null pointer is allowed, and
 * it always sorts at end.
 */
int strord(const void *_a, const void *_b)
{
	char *a = *(char **)_a;
	char *b = *(char **)_b;
	if(a == NULL && b == NULL) return 0;
	if(a == NULL) return 1;
	if(b == NULL) return -1;
	return strcmp(b, a);
}

/*
 * Print an array of ints.
 */
void prints(char *lab, int *ints, int size)
{
	printf("%s: ", lab);
	while(size--) printf("%d ", *ints++);
	putchar('\n');
}

/*
 * Run some sorts.
 */
main()
{
	int intarr[] = { 14, 21, 12, 34, 119, 56, 2, 19, 41 };
	int numints = (sizeof intarr) / (sizeof intarr[0]);
	char *strarr[] = { "snakes", "fish", NULL, "rocks", "water", NULL,
			 "sheep", NULL, NULL, "dogs", "cats" };
	int numstr = (sizeof strarr) / (sizeof strarr[0]);
	int n;

	qsort(intarr, numints, sizeof(int), intasc);
	prints("ascending", intarr, numints);

	qsort(intarr, numints, sizeof(int), intdesc);
	prints("descending", intarr, numints);

	qsort(intarr, numints, sizeof(int), intoddeven);
	prints("peculiar", intarr, numints);

	qsort(strarr, numstr, sizeof(char *), strord);
	for(n = 0; n < numstr; ++n) 
		if(strarr[n]) printf("  %s\n", strarr[n]);
		else printf("  [NULL]\n");
}