("address of") operator. The formal parameters of scanf() now "point to" the new_age and new_weight variables defined in the Person::set() function. scanf() reads values from the standard input and assigns them to the variables "pointed to" by its parameters.
Incidentally, scanf() also returns a value in the conventional sense: the number of items successfully read. As done here, it is common - buy somewhat risky - to ignore this returned value.
