/*
 * ISA 563, Spring 2011
 * Copyleft by Muhammad Abdulla
 */

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

/*
 * arg_passing.c -- Illustrates differences between "call by value" and "call by reference". 
 */

void call_by_val (int m, int n)
{
   printf("inside call_by_val: m = %d, n=%d (before change)\n", m, n); 
   m++;
   n--;
   printf("inside call_by_val: m = %d, n=%d (after change)\n", m, n); 
}

void call_by_ref (int *m, int *n)
{
   int *p;

   printf("inside call_by_ref: m = %d, n=%d (before change)\n", *m, *n); 
   *m += 1;
   *n -= 1;
   printf("inside call_by_ref: m = %d, n=%d (after change)\n", *m, *n); 

   // now try to change the value of the pointers themselves
   p = m;
   m = n;
   n = p;
   printf("inside call_by_ref: m = %d, n=%d (after pointer swap)\n", *m, *n); 
}

int main ( int argc, char *argv[] ) 
{
   int m = 10;
   int n = 20;

   if ( argc == 3 ) {
      m = atoi(argv[1]);
      n = atoi(argv[2]);
   } else if ( argc > 1 ) {
      fprintf(stderr, "Illegal args, going with default values: m = %d, n = %d\n", m, n);
   }

   // calling by value
   call_by_val(m, n);
   printf("after call_by_val: m = %d, n=%d (before change)\n\n", m, n); 

   // calling by reference
   call_by_ref(&m, &n);
   printf("after call_by_ref: m = %d, n=%d (before change)\n", m, n); 

   return 0;
}