Why can const int& bind to an int?

Question

In the C++ primer, I found that const int & can bind with a int object.I don\'t understand that,because I think const int & should bind with a

Answer 1

The value of the variable a which is 0 initially is holded at memory.

If you write later: a=5, it'll set that value in memory to 5.

When you write a reference const int & r = a; you are only saying that r should access that same place in memory where 5 is being hold.

Because a is not const it can modify the value.

This is basically how it works.