#include <iostream>
using namespace std;

void f(int &num)
{
	++num;
}

const int& g(int othernum)
{
	return othernum+3;
}

int main (void)
{
	int x = 3;
	const int y = 4;
	f(x);
	// f(y); produces error message!
	int z = g(5);
	++z;
}