在C ++ ..homework中排队

Question

I have a homework. I try to solve it but I need some help..

1. Use Queue ADT and don't change any of the ADT's functions or procedures. You have to create a structure car that represent the car that will be in the station waiting queue in order to wash car body. Every car has its ID which looks like 124ate [6 character long] and name like eg Superpan and production year as integer variable. In your program you shouldn't call Queue ADT explicitly, instead use global functions to call them (implicitly).
2. Your main program should only have declarations and calls to global functions, no structures should be used.
3. Your output should be firstly looks like the following:
   1. Park new car
   2. Print the number of cars
   3. move earliest coming car
   4. Print All cars
   5. exit

My answer:

#include <iostream>
#include "queue.h"
#include <string>

using namespace std ;

struct car {
    char ID[6];
    int year;
    string name;
}

int main ()
{
    int num;
    car car1;
    Queue <car> q1;

    do {
        cout << "mniu \n"
          << "1. Park new car \n"
          << "2. Print the number of cars \n"
          << "3. move earliest coming car \n"
          << "4. Print All cars \n"
          << "5. exit \n";

        cin >> num;

        switch (num)
        {
        case 1:
            int n;
            cout << "enter id:\n";
            cin >> car1.ID;
            cout << "enter name:\n";
            cin >> car1.name;
            cout << "enter year:\n";
            cin >> car1.year;

            q1.enqueue (car1);
            break;

        case 2:
            cout << "number of cars: " << q1.queueCount();
            break;

        case 3:
            q1.dequeue(car1);
            break;

        case 4:
            while (q1.queueCount()!=0)  
                cout << q1.front();

        case 5:
            cout << "Thank you /n End program";
            break;

        default:
            cout << "failed number. chose from 1 to 5 \n";
        }
    }

    while (num==5);

    return 0;

}

My question:

1. How can I print the queue node by node without deleting it?
2. "Your main program should only have declarations and calls to global functions, no structures should be used." Does it mean my code is wrong because I write everything in main.. I don't understand it.

Answer 1

1. it's a Queue, so you can save the first node in it, and print each element, delete and push it back to the queue, until you see (for the 2nd time!) the 1st element.
2. yes, you shouldn't write all the program in main, but use functions and other files, organized by some logical meaning.

EDIT:

1.

car first = q1.dequeue();
q1.enqueue(first);
  //ADD HERE: print first...
while (q1.peek() != first) {
  car element = q1.dequeue();
  q1.enqueue(first);
  //ADD HERE: print element...
}

add your printing where the comments "ADD HERE:..." are

2. you should add functions like getUserInput() and printQueue() to handle all this scenerios, the main will just call these functions

Answer 2

"Your main program should only have declarations and calls to global functions,"

I believe your instructor is encouraging you to divide your code into individual subroutines, each of which does only one thing. In that style, a typical main might be:

int main() {
    MyDataStruct x;
    ReadInput(x);
    ProcessData(x);
    WriteOutput(x);
}

Notice that there are no for loops in main , no add-up-the-sales-and-copmute-the-tax expressions, nothing in main that requires any processing at all. All of the good stuff is either in your global functions or the methods of your data structures.

Applying that to your program, your main might look like:

int globalExitFlag;
int main() {
    Queue<car> q;
    Car c;
    while( !globalExitFlag ) {
       int cmd;
       cmd = PrintMenuAndAcceptOneAnswer(q, c);
       DoOneCommand(q, c, cmd);
    }
}

Then you can put the guts of your cin reading in PrintMenuAndAcceptOneAnswer , while the printing and queue manipulation lives in DoOneCommand . Of course, you have to write PrintMenuAndAcceptOneAnswer and DoOneCommand yourself. I would further break down those subroutines -- for example, DoOneCommand should call DoPrintAllCars , DoExit , DoParkOneCar , etc.

Finally, I did put a while in this main() , which I think is appropriate. Notice the global variable. I assume that when you process the "exit" command, you'll set that variable to indicate the processing should end.

Good luck, and come back to tell us how your assignment works out for you.