See web reference links at the bottom for more information

• According to the C++ Pocket Reference the ampersand precedes the variable name in a declaration.
• References are used to provide alternative names for the variables. They are declared by placing an ampersand (&) before the variable name.

• Page 341

int rats;
 
// means "reference-to-int"
int & rodents = rats;

• Page 275

int &count;

• Page 277

void squareByReference(int &numberRef)
{
    numberRef  *= numberRef;
}

Some C++ programmers prefer to write:

int& numberRef

To me, this indicates that the placement of the & can be chosen:

• Next to the data type
• Next to the variable

• Wikipedia - Reference (C++)
• IBM - References (C++ only)
• [8] References - C++ FAQ Lite