// A void function returning value via a reference parameter.
#include <iostream>
using namespace std;
void f(float x, float &y);
int main()
{
	float x = 3, y;
	f(x,y);
	cout << y << endl;
	return 0;
}

void f(float x, float& y /* y is an output parameter */)
{
	y = x * x; 
}