what is this & on line 17 and 22 and why is it there? (c++)

6 using namespace std: /1 Holds data for an inventory item /1 Part number /1 Units on hand 8 struct Invitem 60 61 void 62 10 int partNum 11 string description Item description Co 63 64 65 12 int onHand; 13 double price: 11 Unit price 14 ): 15 67 68 16 /1 Function prototypes 17 void getitemData (InvItem &): // Function getitemData will receive an 18 / InvItem structure passed to it by /I reference so new values can be stored /I in its member variables 19 20 21 Prog Enter Ente Ente Ente 22 void showItem (const InvItem &) 23 // Function showItem will receive arn 24 InvItem structure passed to it as a /I constant reference because showItem /I just needs display member variable /I values, not change them 25 Par Des Un 26 27 28 int main) 29 f 30 InvItem part; 31 32 getItemData (part); // Define an InvItem structure variable. 33 showItem (part): 34 35 36 return 0; (program continues)