int main() {
	int x = 1;
	
	// ======= pointer =======
	int *ptr_x = &x;
	// or
	// int *ptr_x;
	// ptr_x = &x;  here &x means address of x
	
	// use the pointer syntax to manipulate
	*ptr_x = *ptr_x + 1;
	
	// ======= reference =======
	// ref_x is a reference to an existing variable
	int& ref_x = x;
	ref_x = ref_x + 1;
	
	return 0;
}