Help required regarding queue using linked list

[SAM2012]

I have a queue class code is given below:

struct ListNode
{
    ListNode(int value);
    int value;
    ListNode* next;
}; 
ListNode::ListNode(int value): value(value), next(nullptr) {}

public class queue
{
public:
    queue();
    ~queue();
    bool Empty() const;
    int Next() const;
    void Enqueue(int value);
    void Dequeue();
        void DisplayAll() const;
        int getP() const;


      private:
    // Disable copying to keep the example simple

   queue(queue const& obj);

    ListNode* head;
    ListNode* tail;
    gcroot<String^> name; // Added this
};

queue::queue():head(nullptr), tail(nullptr) {}

queue::~queue()
{
    while (head != nullptr)
    {
        Dequeue();
    }
}


bool queue::Empty() const
{
    return head == nullptr;
}

int queue::Next() const
{
    return head->value;
}

void queue::Enqueue(int value)
{
    if (head == nullptr)
    {
        head = tail = new ListNode(value);
    }
    else
    {
        tail->next = new ListNode(value);
        tail = tail->next;
    }
}

void queue::Dequeue()
{
    ListNode* temp = head->next;
    delete head;
    head = temp;
}

void queue::DisplayAll() const
{
    for (ListNode* p = head; p; p = p->next)
    {
        Console::WriteLine("the element is {0}", p->value);
    }

}

I need some help regarding queues operation, which I already have made. To help explain the problem you need to look at this code and the queue operations given in the above posted code.

if(Analysis[no].priority==1)
         cat1->Enqueue(no);
      else if(Analysis[no].priority==2)
         cat2->Enqueue(no);
      else if(Analysis[no].priority==3)
         cat3->Enqueue(no);
      while(!(cat1->Empty()))
         {
            p= cat1->Next();
            TimDep= currtime+expntl();
            slist->Add(TimDep,"D");
            Analysis[p].TEsf=TimDep;
         }

consider we have 3 queues cat1, cat2, cat 3. I want to insert items with pririty 1,2,3 respectively. which I am doing via this code. Now I want to process these inserted messages(or items "no"). First I want to process all messages in queue "cat1" and dequeue them one by one untill its empty, then it should move to "cat2" and same process and then to "cat3". I am stuck in the process of iterating through each element of queue how can I do that? can you help me please!!!!

[rubberman]

I won't go beyond the struct declaration. You are using the same name for the constructor argument as you are using for the member variable. DON'T DO THAT! As a good practice, use m_ as a prefix for member variables, so instead of value, the member variable name is m_value, or m_pNext for the list link. The 'p' in m_pNext indicates that you intend for it to be a pointer.

As for your particular usage problem, you are only showing a small part of your code, and not enough to determine what you are really doing. A fuller explanation of what you are trying to accomplish would be good. It sounds like you want to process queue 1, then queue 2, etc in order? Is that correct?

[SAM2012]

yes you are right, Can you help me to write the code well. I mean only the iteration part of all the items of one queue then second and then third.

[SAM2012]

Hi,

I have written some code for priority queuing but this code is only processing items with priority 1. Can you help with this code please.......I am helpless

no=noofmsg-1;
     if(Analysis[no].prio==1)
         cat1->Enqueue(no);

     else if(Analysis[no].prio==2)
         cat2->Enqueue(no);

     else if(Analysis[no].prio==3)
         cat3->Enqueue(no);

      while(!(cat1->Empty()))
         {
            p= cat1->Next();
            TimDep= currtime+expntl();
           // slist->Add(TimDep,"D");

            Analysis[p].TEsf=TimDep;
            Console::WriteLine(" the value at  is  Analysis{0} is {1}", p, Analysis[p].TEsf );
            /*avg1= Analysis[p].TEsf-Analysis[p].TEa;
            Console::WriteLine(" The priority 1 messages has a waiting time of {0} ", avg1 );*/
            cat1->Dequeue();

         }

  if(cat1->Empty())
     {
      while(!(cat2->Empty()))
         {
            p= cat2->Next();
            TimDep= currtime+expntl();
            //slist->Add(TimDep,"D");

            Analysis[p].TEsf=TimDep;
            //Console::WriteLine(" the value at  is  Analysis{0} is {1}", p, Analysis[p].TEsf );
            cat2->Dequeue();
         }
      }
   if((cat1->Empty())&&(cat2->Empty()))
     {
      while(!(cat3->Empty()))
         {
            p= cat3->Next();
            TimDep= currtime+expntl();
            //slist->Add(TimDep,"D");

            Analysis[p].TEsf=TimDep;
            //Console::WriteLine(" the value at  is  Analysis{0} is {1}", p, Analysis[p].TEsf );
            cat3->Dequeue();
         }
      }

[WaltP]

See comments:

  while(!(cat1->Empty()))
  {
        // process queue 1
  }

  if(cat1->Empty())    // Didn't you just empty queue 1? 
  {                    // Why do you need to test if it's empty?
     while(!(cat2->Empty()))
     {
        // process queue 2
     }
  }

I don't see a definition for nullptr. Did you define it to be FALSE or 0? Or is it a C++ definition that you are assuming to be FALSE/0?

Output values at key places in the code to see if the values are correct and the code is making the decisions you expect.

[SAM2012]

Thankyou very much for your reply. I have seen the use of the nullptr keyword instead of 0 to indicate a null pointer value.

is that OK to write

while(!(cat1->Empty()))

But still I am not getting the results what I want. PLEASE HELP !!!!!!!!!!!!!!!!!!!!!!!!!