간단한 c++ reference(참조자) 예제인데 에러가 나네요

/*   Reference(참조자)   */
#include<iostream>
 
 
int main(void)
{
	int num1 = 1020;
	int &num2 = num1;
 
	num2 = 3047;
	cout<<"VAL: "<<num1<<endl;
	cout<<"REF: "<<num2<<endl;
 
	cout<<"VAL: "<<&num1<<endl;
	cout<<"REF: "<<&num2<<endl;
 
	return 0;
}