The following tests are made on solaris 5.10 platform.
This is the example of the decrement(--) for short index of array:
/*********************************************************/
#include <stdio.h>
int main()
{
	int 				aryHuowq[3] = {0};
	short 				nIndex = 2; /* nIndex is short */

	aryHuowq[nIndex--] = nIndex + 1;
	printf("array[%d] : %d\n", nIndex+1, aryHuowq[nIndex+1]);
	return 0;
}
/*****************************************************************/
/* The result is "array[2] : 2", but it should be "array[2] : 3" */
/*****************************************************************/

If nIndex is type of int, then the result is "array[2] : 3".