#include <iostream>
#include <cstdlib>
using namespace std;

//The function f can not change the value of its first argument,
//but it could change the value of its second argument.
void f(int i, int& r);

int main()
{
	int a {10};
	int b {20};

	f(a, b);  //The function f increments b but not a. 

	cout << "a == " << a << "\n"
		<< "b == " << b << "\n";

	return EXIT_SUCCESS;
}

//Demonstrate pass-by-value vs. pass-by-reference.
//The initial value of i is a copy of the value of a.
//But the value of r is always the same value as the value of b.

void f(int i, int& r)
{
	++i;   //Increments i, but this has no effect on the value of a.
	++r;   //increments b.

	cout << "i == " << i << "\n"
		<< "r == " << r << "\n\n";   //Outputs the value of b.
}