#include <iostream>
using namespace std;

void Func(int& x, const int& y);    // x CAN be changed.  y cannot


int main()
{
   int a1 = 5, a2 = 8;
   cout << "a1 = " << a1 << "\ta2 = " << a2 << '\n';

   // legal call   
   Func(a1, a2);
   cout << "a1 = " << a1 << "\ta2 = " << a2 << '\n';

   // legal call
   Func(a1, 20);
   cout << "a1 = " << a1 << "\ta2 = " << a2 << '\n';

/*
   // ILLEGAL call
   Func(20, a2);
   cout << "a1 = " << a1 << "\ta2 = " << a2 << '\n';
*/

   return 0;
}


void Func(int& x, const int& y)
// x CAN be changed.  y cannot
{
   x = x * 2;
//   y = y * 2;		// this is illegal

   cout << "x = " << x << '\n';
   cout << "y = " << y << '\n';
}