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

void increment(int *p, int& r);

int main()
{
	int i = 10;
	int j = 20;

	//Obvious that line 14 can change i,
	//dangerously unobvious that line 14 can also change j.
	increment(&i, j);

	cout << "i == " << i << "\n"
		<< "j == " << j << "\n";

	return EXIT_SUCCESS;
}

void increment(int *p, int& r)
{
	++*p;   //means *p = *p + 1
	++r;    //means r = r + 1
}