/* EXAMPLE PROGRAM#1:  Parameter Passing (refval.cc)
 *   
 * CS302-11/21 - Spring 96
 *
 *   This program demonstrates value parameters vs. reference parameters.
 * Its sole purpose is to demonstrate the difference between the two.  
 *
 * This file can be found at 
 *      http://www.cs.wisc.edu/~hcl/cs302/refval.cc
 */

#include <iostream.h>

// function prototypes
void fun1(int& x);       
int fun2(int y);
void fun3(int& x,int& y);  
void fun4(int& x,int y);

void printints(int,int,int);

main()
{
   int a=0, b=5, c=10;     // Start 

   cout << endl << "In the order:  a, b, c. " << endl;
   printints(a,b,c);

   fun1(a);               // Section 1
   fun1(b);
   fun1(c);
   printints(a,b,c);

   cout << " fun2(" << a << ") returns: " << fun2(a) << endl;    // Section 2           
   cout << " fun2(" << b << ") returns: " << fun2(b) << endl;
   cout << " fun2(" << c << ") returns: " << fun2(c) << endl;
   cout << " fun2(20) returns: " << fun2(20) << endl;     // fun2(20) <=> fun2(a)
   printints(a,b,c);

   fun3(a,b);              // Section 3
   fun3(b,c);
   printints(a,b,c); 

   fun3(a,b);              // Section 4
   printints(a,b,c);

   fun3(b,a);              // Section 5
   printints(a,b,c);

   cout << endl << "Switch order:  b, c, a. " << endl;   // depends on arg order
   printints(b,c,a);
}                          // main() ends





// *** FUNCTION DEFINTIONS BEGIN HERE ***

void fun1(int& x)    // this is a reference parameter, so whatever happens to x
{                    // will also happen to whatever variable is passed to it.
  x = x + 20;
}

int fun2(int y)      // this is a value parameter, so an *value* is coming in and
{                    // will be copied into the new, and distinct, location y.
  y = y + 12;        // The function returns the result, but this has no effect
  return y;          // on the calling argument.
}

void fun3(int& x, int& y)  // two reference parameters, so both args are affected back
{                          // in main()
  x = x / 2;
  y = y / 3;
}

void fun4(int& x, int y)   // x is a reference parameter, so its argument will change
{                          // back in main(), but y is a value parameter, so its argument
  x = x + 100;             // will not change.      
  y = y + 500; 
}

void printints(int q, int r, int s)
{
  cout << "  " << q << ", " << r << ", " << s << endl;
}