Computer science c++ vector/void help

Question

An airline uses a computer system to maintain flight sales information. For planning purposes, the airline must know what seats are on the plane, what seats are available, what seats are booked, and must have the ability to change the status of a seat from available to booked and vice versa. For this assignment, you will be implementing some of the functionality of the airline computer system. You will need to implement the following steps.

(1) Create the initial vectors for seats on the plane and seat status. You may assume that the plane has rows 1 through 5 and each row has seat A through D. The seat status is a 0 if the seat is available or a 1 if the seat is booked, and, therefore, not available.

(2) Implement a menu of options for the user. Following the initial setup of the vectors, the program outputs the menu. The program should also output the menu again after a user chooses an option. The program ends when the user chooses the option to Quit.

Ex:

Menu options:

1. Display All Seats Status:

2. Total Number of Available Seats:

3. Display Available Seats:

4. Book Seat:

5. Cancel Seat:

6. Change Seat:

7. Quit:

Please select an option:

(3) Implement the "Display All Seats Status" menu option. Be sure to write a separate function for each menu option.

Ex:

Seat Status

1A 0

1B 0

1C 0

1D 0

2A 0

...

(4) Implement the "Total Number of Available Seats" menu option.

Ex:

Number of available seats: 20

(5) Implement the "Display Available Seats" menu option. This function should show a list of available seats.

Ex:

Available seats:

1A

1B

1C

1D

2A

...

(6) Implement the "Book Seat" menu option. This function should take in the seat to book and then should change the status of that seat to unavailable. After the function, the status of all seats should be displayed.

Ex:

Enter seat to book: 1A

Seat Status

1A 1

1B 0

1C 0

1D 0

2A 0

...

(7) Add logic to the "Book Seat" menu option that will not allow the user to book a seat that is already booked.

Ex:

Enter seat to book: 1A

That seat is already taken.

Enter seat to book: 1B

Seat Status

1A 1

1B 1

1C 0

1D 0

2A 0

...

Answer 1

The clue to what is going wrong is right there in your title. If you write a menu function like

void bookSeat(vector<int> status)

then C++ hands that function its own private copy of the vector. You mark the seat as booked inside the function, the function ends, the copy gets thrown away, and main is still holding all zeros. One ampersand is the whole fix:

void bookSeat(const vector<string> &seats, vector<int> &status)

Now the function is changing the same vector that main is holding, so the booking sticks. Anything that only reads, like displaying the seats or counting the open ones, can take const references and still be void, since it prints instead of returning a value.

For the setup, notice the problem is pointing you at two vectors that run in parallel. Use a nested loop over rows 1 to 5 and letters A to D so that seats holds 1A, 1B, 1C, 1D, 2A and so on, and build status as twenty zeros in that same order. The order is really the whole trick, because position i in seats always describes the same seat as position i in status.

Once they line up you never have to search the vector at all. If the user types the seat as a string s, then s[0] - '0' gives you the row number and s[1] gives you the letter, so

int index = (s[0] - '0' - 1) * 4 + (s[1] - 'A');

turns 1A into 0, 2A into 4 and 5D into 19. After that each menu option is only a few lines. Displaying all seats is a loop printing seats[i] and status[i], the available count is a loop counting the positions where status[i] is 0, booking is checking whether status[index] is already 1 before you set it, and cancelling is that same check in reverse. I would write just the display function with the ampersand first and confirm in main that the change actually shows up, because once that part clicks the other six options all follow the same shape.