/*
 * SWAP -- demonstrate how pointers work as parameters to functions
 *
 * Usage: swap
 *
 * Inputs: none
 *
 * Outputs: lines showing 2 values before and after swapping with and
 *     		without pointers
 *
 * Exit Code: 0 (always succeeds)
 *
 * written for ECS 030, Fall 2015
 * 
 * Matt Bishop, Oct. 14, 2015
 *      revision from an earlier program
 *
 */
#include <stdio.h>

/*
 * swap two elements (no pointers)
 */
void npswap(int x, int y)
{
	int temp;		/* temporary */
	/*
	 * show what they are on entry
	 */
	printf("begin npswap: elem1 is %d, elem2 is %d\n", x, y);
	/*
	 * do the swap
	 */
	temp = x;
	x = y;
	y = temp;
	/*
	 * show they were exchanged
	 */
	printf("  end npswap: elem1 is %d, elem2 is %d\n", x, y);
}

/*
 * swap two elements (pointers)
 */
void pswap(int *x, int *y)
{
	int temp;		/* temporary */
	/*
	 * show what they are on entry
	 */
	printf("begin  pswap: elem1 is %d, elem2 is %d\n", *x, *y);
	/*
	 * do the swap
	 */
	temp = *x;
	*x = *y;
	*y = temp;
	/*
	 * show they were exchanged
	 */
	printf("  end  pswap: elem1 is %d, elem2 is %d\n", *x, *y);
}
 
/*
 * this is to show that everything is call by value
 * so you need to simulate call by reference
 * it uses swapping
 */
int main(void)
{
	int elem1 = 4;			/* first element */
	int elem2 = 5;			/* second element */
	/*
	 * say what you're starting with
	 */
	printf("     initial: elem1 is %d, elem2 is %d\n",
								elem1, elem2);
	/*
	 * use the non-pointer swap and print the results
	 */
	npswap(elem1, elem2);
	printf("after npswap: elem1 is %d, elem2 is %d\n",
								elem1, elem2);
	/*
	 * use the pointer swap and print the results
	 */
	pswap(&elem1, &elem2);
	printf("after  pswap: elem1 is %d, elem2 is %d\n",
								elem1, elem2);
	/*
	 * say goodbye
	 */
	return(0);
}