Use of structure pointers as function

Program 59) The price and quantity of items stocked in a store everyday. They may either increase or decrease. This program reads the incremental values of price and quantity and computes the total value of the item in stock.
The program illustrates the use of structure pointers as a function parameters. &item, the address of the structure item, is passed to the functions update() and mul(). The formal argument product and stock, which recieve the value of &item, are declared as pointers of type struct stores.

                                 PROGRAM

struct stores
{
       char name [20] ;
       float price ;
       int quantity ;
} ;
main ( )
 {
         void update (struct stores *, float, int) ;
         float         p_increment, value ;
         int            q_increment ;

        struct stores item = {"XYZ", 25.75, 12) ;
        struct stores *ptr = &item ;

       printf ("\Input increment value:") ;
       printf (" price increment and quantity increment\n") ;
       scanf ("%f %d, &p_increment, &q-increment) ;

/*     - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - -     /*
       update (&item, p_increment, q_increment) ;
/*     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -      /*
       printf ("Updated values of item\n\n") ;
       printf ("Name        : %s\n", ptr->name) ;
       printf ("price         : %f\n", ptr_>price) ;
       printf ("Quantity   : %d\n", ptr_>quantity) ;

/*     - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -     /*
       value  = mul (& item) ;
/*     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -        /*
       printf ("\nValue of the item = %f\n", value) ;
 }

 void update (struct stores *product, float p, int q) 
 {
          product->price += p ;
          product->quantity += q ;
 }
 float mul (struct stores *stock)
 {
         return (stock->price * stock->quantity) ;
 }


                                Output

Input increment value: price increment and quantity 
                                                                      increment
10  12
Updated value of item

Name      : XYZ
price       : 35.750000
Quantity : 24

Value of the item = 858.000000