#include <stdio.h>

void bad_swap (int x, int y);
void swap (int *x, int *y);

int main ()
{
	int a = 1, b = 2;
	int *p, *q, *r;

	p = &a;
	q = &b;
	r = &a;

	printf("The following commands were given:\n");
	printf("1.  int a = 1, b = 2\n");
	printf("2.  int *p, *q, *r\n");
	printf("3.  int p = &a\n");
	printf("4.  int q = &b\n");
	printf("5.  int r = &a\n");

	printf("\nHere are the values prior to the first operation:\n");
	printf("          a = %10d     b = %10d\n", a, b);
	printf("          p = %10d     q = %10d     r = %10d\n", p, q, r);
	printf("         *p = %10d    *q = %10d    *r = %10d\n", *p, *q, *r);

	printf("\nThe following is an attempt to assign the value of 'b' to 'a' using pointers:\n");
	p = q;

	printf("The following command was given:\n");
	printf("1.  p = q\n");

	printf("\nHere are the values after the first operation:\n");
     printf("          a = %10d     b = %10d\n", a, b);
	printf("          p = %10d     q = %10d     r = %10d\n", p, q, r);
	printf("         *p = %10d    *q = %10d    *r = %10d\n", *p, *q, *r);

	printf("\nAs can be seen from the numbers above, all that happened was\n");
	printf("that 'p' became a pointer to 'b.'  The value of 'a' remained unchanged.\n");

	printf("Press RETURN to continue...");
	getchar();

	printf("\nAll values have been returned to normal.\n");
	p = r;

	printf("\nHere are the values prior to the second operation:\n");
	printf("          a = %10d     b = %10d\n", a, b);
	printf("          p = %10d     q = %10d     r = %10d\n", p, q, r);
	printf("         *p = %10d    *q = %10d    *r = %10d\n", *p, *q, *r);

	printf("\nThe following is a demonstration that variables are passed by\n");
	printf("value to functions; thus, preventing the function from making\n");
	printf("changes to the ACTUAL variable.\n");

	printf("\nThe following function call was issued:\n");
	printf("1.  bad_swap (a, b)\n");
	bad_swap (a, b);

	printf("\nHere are the values after the second operation:\n");
     printf("          a = %10d     b = %10d\n", a, b);
	printf("          p = %10d     q = %10d     r = %10d\n", p, q, r);
	printf("         *p = %10d    *q = %10d    *r = %10d\n", *p, *q, *r);

	printf("\nAs can be seen from the numbers above, nothing happened to the\n");
	printf("ACTUAL variables within the main program.\n");

	printf("Press RETURN to continue...");
	getchar();

	printf("\nAll values have been returned to normal.\n");

	printf("\nHere are the values prior to the third operation:\n");
	printf("          a = %10d     b = %10d\n", a, b);
	printf("          p = %10d     q = %10d     r = %10d\n", p, q, r);
	printf("         *p = %10d    *q = %10d    *r = %10d\n", *p, *q, *r);

	printf("\nThe following is a demonstration of a properly executed\n");
	printf("swap function. This implementation employs the use of pointers\n");
	printf("passed to the function, so that the addresses can be changed.\n");
	
	printf("\nThe following function call was issued:\n");
	printf("1.  swap (p, q);\n");
	swap (p, q);

     printf("\nHere are the values after the third operation:\n");
	printf("          a = %10d     b = %10d\n", a, b);
	printf("          p = %10d     q = %10d     r = %10d\n", p, q, r);
	printf("         *p = %10d    *q = %10d    *r = %10d\n", *p, *q, *r);
	printf("\n\n\n\n\n");

	return (0);
}

void bad_swap (int x, int y)
{
	int temp;

	printf("This line occurs inside the function before swap: x(a) = %d     y(b) = %d\n", x, y);
	temp = x;
	x = y;
	y = temp;
	printf("This line occurs inside the function after swap : x(a) = %d     y(b) = %d\n", x, y);

	return;
}

void swap (int *x, int *y)
{
	int temp;

	temp = *x;
	*x = *y;
	*y = temp;

	return;
}