Q1: Is add_salad supposed to be another function that we call from main?  

Q2: Can you give me any helpful hints on how to go about solving
this because I've spent hours trying all sorts of methods but I have failed 
so far.

Q3: How can I put a call-by-reference parameter into:
    double add_salad (char deliver, int n_person)?

Q4: What is the proper way of writing inline function?

Q5: What's wrong with my inline function?
    inline void add_tip (price) {return price *= 1.15;}

Q6: I know that void shouldn't have a value to return...but if it
does't...what does it do here?     
    inline void add_tip (price) {return price *= 1.15;}


Q1: Is add_salad supposed to be another function that we call from main?  

A1: Yes.  Look at the PA (Programming Assignments) handout, page 7 Step b)   
It lists the function declarations as:
  double add_salad(void);
  double add_salad(char deliver, int n_person = 10);
Look at Step e).  It talks about add_salad() in great detail.
Look at HINTS at the bottom of the page.  Step 4) and then Step 5).


Q2: Can you give me any helpful hints on how to go about solving this because 
    I've spent hours trying all sorts of methods but I have failed so far.

A2: How about your notes from lecture?  Did you write down the information
    from the blackboard specifically on PA#5?
    This was about 20 minutes of explanation, pseudocode,and hints.  You also 
    want to see the Proctors for specific questions.  Also office hours.
    Maybe look at another student's notes for PA#5.


Q3: How can I put a call-by-reference parameter into:
                    double add_salad (char deliver, int n_person)?

A3: PA#5 asks to use only reference types (call by reference parameter)
    only with "inline void add_tip(double & rprice);"

Therefore NOT with "double add_salad (char deliver, int n_person = 10);

You will have to pass parameters (call by value).  With any of these function 
calls:
   salad_price = add_salad ( ans );               // default 10 persons
   salad_price = add_salad ( ans, num_person);

Note:
   salad_price = add_salad ( ); // calls void add_salad(void); for 20 persons


Q4: What is the proper way of writing inline function.

A4: Function declaration from PA handout, page 7, Step b)
    inline void add_tip ( double  & rprice);

To make it inline, just place keyword "inline" in front:
a) If you have both function declaration and function definition 
   OR
b) If you have only a function definition placed before its call.


Q5: What's wrong with my inline function?:
    inline void add_tip (price) {return price *= 1.15;}

A5: Remember, 1st line of function definition (header) is like the function 
    declaration.
      inline void add_tip ( double  & rprice) 
      { ... }


Q6: I know that void shouldn't have a value to return...but if it does't...what
    does it do here?     inline void add_tip (price) {return price *= 1.15;}

A6: Right, void does not return a value, therefore the compiler complains 
because you told it NOT to save any space for a return value.  So it didn't.
AND now you are trying to return a value!

Remember you are using a reference type parameter.  It is an alias for your 
argument you passed to the function.  Therefore, you passed in the price from 
main().  add_tip() is accessing the original value and returns NO value.  Do 
all the same function body AND do *NOT* use the keyword "return".