R1 is a reference bound to 1

[EnigmaticZee]

ri is a reference bound to i so how come it prints 10, 10 ?

  int i, &ri = i;
i = 5; ri = 10;
std::cout << i << " " << ri << std::endl;

[Peter87]

ri refers to i so when you do ri = 10; you are setting the value of i to 10.

[EnigmaticZee]

It's ri = 10 and nowhere it says i = ri

[Peter87]

See that & on the first line? That means ri is a reference to i. You can think of ri as an alternative name for i. When you use ri in the code you are actually using i.