Reversing elements in a Queue Problem

Question

NinjaLink -2 Posting Pro in Training

14 Years Ago

Hello, I need help reversing elements in a queue using Recursion. My problem is that when I print out the reverse, it does not show the numbers on the screen. However my program compiles and runs. My question is...How come the numbers in reverse are not showing? Thanks for anyone who helps!

Current output:

The original elements in the queue are... 5 10 15 20
The reverse elements in the queue are...

Expected output:

The original elements in the queue are... 5 10 15 20
The reverse elements in the queue are... 20 15 10 5

Program:

#include <fstream>
#include <sstream>
#include "queue.h"


int ReverseQueue(int numbers);


using namespace std;

int main()
{
    
ifstream inData("input.txt"); 
ofstream outData("output.txt");
stringstream ss;
string line;
int numbers;

outData<<"The original elements in the queue are... ";

  while(getline(inData, line))
  {
  ss << line;
  }
  while(ss>>numbers)
  { 
   outData<<" "<<numbers;       
  }
  outData<<endl;
  
outData<<"The reverse elements in the queue are... ";

 while(getline(inData, line))
  {
  ss << line;
  }
  while(ss>>numbers)
  { 
   ReverseQueue(numbers);                  
   outData<<" "<<numbers;       
  }     

inData.close();
outData.close(); 

system ("PAUSE");
return 0;
}


int ReverseQueue(int numbers)
{

queueType<int> Queue1;
queueType<int> Queue2; 
queueType<int> Queue3;   
     

while (!Queue1.isEmptyQueue())
{
   Queue1.deleteQueue();
   Queue2.addQueue(numbers);
   Queue3.addQueue(numbers);

}

while (!Queue3.isEmptyQueue())
{
   Queue3.deleteQueue();
   Queue1.addQueue(numbers);
}

return ReverseQueue(numbers);
}

queue.h

#ifndef H_queueType
#define H_queueType

#include <iostream>
#include <cassert>

using namespace std;

template<class Type>
class queueType // public queueADT<Type>
{
      public:
             const queueType<Type>& operator=(const queueType<Type>&);
             bool isEmptyQueue() const;
             bool isFullQueue() const;
             void initializeQueue();
             Type front();
             Type back();
             void addQueue(const Type& queueElement);
             void deleteQueue();
             queueType(int queueSize = 100);
             queueType(const queueType<Type>& otherQueue);
             ~queueType();
             bool operator== (const queueType<Type>&);
             bool operator!= (const queueType<Type>&);
             void deleteBackOfQueue();
             void deleteFrontOfQueue();
             void printQueue();
             
      private:
              int maxQueueSize;
              int count;
              int queueFront;
              int queueRear;
              Type *list;
              bool isEqual(const queueType<Type>&);
};

template<class Type>
bool queueType<Type>::isEmptyQueue() const
{
     return (count == 0);
}

template<class Type>
bool queueType<Type>::isFullQueue() const
{
     return (count == maxQueueSize);
}

template<class Type>
void queueType<Type>::initializeQueue()
{
     queueFront = 0;
     queueRear = maxQueueSize - 1;
     count = 0;
}

template<class Type>
Type queueType<Type>::front()
{
     assert(!isEmptyQueue());
     return list[queueFront];
}

template<class Type>
Type queueType<Type>::back()
{
     assert(!isEmptyQueue());
     return list[queueRear];
}

template<class Type>
void queueType<Type>::addQueue(const Type& newElement)
{
     if (!isFullQueue())
     {
       queueRear = (queueRear + 1) % maxQueueSize;
       
       count++;
       list[queueRear] = newElement;
     }
     
     else
       cout<< "Cannot add to a full queue."<<endl;
}

template<class Type>
void queueType<Type>::deleteQueue()
{
     if (!isEmptyQueue())
     {
       count--;
       queueFront = (queueFront + 1) % maxQueueSize;
     }
     
     else
     cout <<"Cannot remove from an empty queue"<<endl;
     
}

template<class Type>
queueType<Type>::queueType(int queueSize)
{
  if (queueSize <= 0)
  {
    cout<<"Size of the array to hold the queue must "
        <<"be positive."<<endl;
    cout<<"Creating an array of size 100."<<endl;
    
    maxQueueSize = 100;
  }
  
  else
  
     maxQueueSize = queueSize;
     
     queueFront = 0;
     queueRear = maxQueueSize - 1;
     count = 0;
     list = new Type[maxQueueSize];
}

template<class Type>
queueType<Type>::~queueType()
{
   delete [] list;
}


template<class Type>
bool queueType<Type>::isEqual(const queueType<Type>& otherQueue) 
{
bool bRet = false;

if (otherQueue.maxQueueSize == maxQueueSize && otherQueue.queueFront == queueFront)
{
bRet = true;
for (int j = 0; j < queueFront; ++j) 
{
if (otherQueue.list[j] != list[j]) 
{
// cout << "!=( " << j << ") " << otherStack.list[j] << "!=" << list[j];
bRet = false;
break;
}
}
}
return bRet;
}

template<class Type>
bool queueType<Type>::operator==(const queueType<Type>& otherQueue) 
{
return isEqual(otherQueue);
}

template<class Type>
bool queueType<Type>::operator!=(const queueType<Type>& otherQueue) 
{
return !isEqual(otherQueue);
}



template<class Type>
void queueType<Type>::deleteBackOfQueue()
{
if (!isEmptyQueue())
{
count--;
queueRear = (queueRear - 1) % maxQueueSize;
}
else
cout <<"Cannot remove from an empty queue"<<endl;
}

template<class Type>
void queueType<Type>::deleteFrontOfQueue()
{
if (!isEmptyQueue())
{
count--;
queueFront = (queueFront - 1) % maxQueueSize;
}
else
cout <<"Cannot remove from an empty queue"<<endl;
}

template<class Type>
void queueType<Type>::printQueue()
{
         
for (int i=queueFront; i<queueRear; ++i)
{
    cout<<" "<<list[i];
} 

}


#endif

c++

2 Contributors
2 Replies
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Latest Post 14 Years Ago Latest Post by NinjaLink

All 2 Replies

JasonHippy 739 Practically a Master Poster

14 Years Ago

From looking at the code, it seems to me that if you run your debugger and step through the program you'll find that line 34 will fail to read anything from the input file.

The reason for this is because by this point you've already read the entire file, so your input stream inData is pointing to the end of the file. So what you need to do is reset inData to point to the start of the file.
If you close the input file and then reopen it again between lines 32 and 34, that should achieve the desired effect.
There are probably other ways, but I can't think of any offhand!

However, the failure to read from the file is the least of your problems.
Once you've fixed the read problem, when your call to ReverseQueue is made, your program will get stuck in infinite recursion. Your program will recursively call ReverseQueue until the program runs out of memory and crashes.

Your program does not fulfil the criteria you need to meet, it doesn't reverse the queue, so you're going to need to rethink your program logic.

Wouldn't it make sense to read your input file once, sending the values into an instance of your queue class? Then perhaps iterate through your queue to output the original values to the output file before passing your queue to a recursive function to reverse the queue, before finally outputting the final values to the output file.
I'll leave it to you to decide what to do in the recursive function, but don't forget to include some way of breaking out of the recursion. As we've already seen infinite recursion isn't good!

Cheers for now,
Jas.

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NinjaLink -2 Posting Pro in Training · Answer 1 · 2009-11-13T11:06:10+00:00

Thanks Jason.

I am currently having a problem. I feel that I did everything right to try to get the numbers in reverse, however, I am only getting the last element in reverse so far and none of the other elements are showing! Can you please help me fix this problem?

Recent output:

The original elements in the queue are... 5 10 15 20
The reverse elements in the queue are... 20