const int i = 10;
const int &ref = i;

int &ref1 = i; // error: nonconst reference to a const object

// legal for const references only
int i = 10;
const int & ref = 42;
const int & ref1 = r + i;
double d = 3.14;
const int &ref2 = d;

int temp = d;
const int &ref2 = temp; // bind ref2 to temporary