C++ Programmer Question:

Appending an ampersand (&) to the end of datatype makes a variable eligible to use as reference variable.

int a = 20;
int& b = a;

The first statement initializes a an integer variable a. Second statement creates an integer reference initialized to variable a
Take a look at the below example to see how reference variables work.

int main ()
{
int a;
int& b = a;

a = 10;
cout << "Value of a : " << a << endl;
cout << "Value of a reference (b) : " << b << endl;

b = 20;
cout << "Value of a : " << a << endl;
cout << "Value of a reference (b) : " << b << endl;

return 0;
}
Above code creates following output.

Value of a : 10
Value of a reference (b) : 10
Value of a : 20
Value of a reference (b) : 20