Urgent help: print elements in queue

J

j_depp_99

Thanks to those guys who helped me out yesterday. I have one more
problem; my print function for the queue program doesnt work and goes
into an endless loop. Also I am unable to calculate the length of my
queue. I started getting compilation errors when I included a length
function.
<code>

template<class ItemType>
void Queue<ItemType>::MakeEmpty()
{
rear = maxQue - 1;
front = maxQue - 1;
}

template<class ItemType>
bool Queue<ItemType>::IsEmpty()
{
return (rear==front);
}

template<class ItemType>
bool Queue<ItemType>::IsFull()
{
return ((rear+1) % maxQue == front);
}

template<class ItemType>
int Queue<ItemType>::length()
{
return 0; // I dont know what to put here
}

template<class ItemType>
void Queue<ItemType>::print()
{
int current;
current = rear;
do{
current = (current + 1) % maxQue;
std::cout << items[current] << std::endl;
}while(current != front);
}

// Main function items

IntQueue.Enqueue(1);
IntQueue.Enqueue(2);
IntQueue.Enqueue(3);
IntQueue.Enqueue(4);
cout << "int length 3 = " << IntQueue.length() << endl;
IntQueue.Dequeue(x);
cout << "int length 4 = " << IntQueue.length() << endl;
IntQueue.Print();

</code>

my length function has no code and I dont know what to put in there.
 
M

mlimber

Thanks to those guys who helped me out yesterday. I have one more
problem; my print function for the queue program doesnt work and goes
into an endless loop. Also I am unable to calculate the length of my
queue. I started getting compilation errors when I included a length
function.
<code>

template<class ItemType>
void Queue<ItemType>::MakeEmpty()
{
rear = maxQue - 1;
front = maxQue - 1;

}

template<class ItemType>
bool Queue<ItemType>::IsEmpty()
{
return (rear==front);

}

template<class ItemType>
bool Queue<ItemType>::IsFull()
{
return ((rear+1) % maxQue == front);

}

template<class ItemType>
int Queue<ItemType>::length()
{
return 0; // I dont know what to put here

}

template<class ItemType>
void Queue<ItemType>::print()
{
int current;
current = rear;
do{
current = (current + 1) % maxQue;
std::cout << items[current] << std::endl;
}while(current != front);

}

// Main function items

IntQueue.Enqueue(1);
IntQueue.Enqueue(2);
IntQueue.Enqueue(3);
IntQueue.Enqueue(4);
cout << "int length 3 = " << IntQueue.length() << endl;
IntQueue.Dequeue(x);
cout << "int length 4 = " << IntQueue.length() << endl;
IntQueue.Print();

</code>

my length function has no code and I dont know what to put in there.
Click to expand...

You haven't posted sufficient code here to allow us to give a sensible
answer. Help us help you. Read and obey this FAQ:

http://www.parashift.com/c++-faq-lite/how-to-post.html#faq-5.8

Cheers! --M
 
J

j_depp_99

Sorry about that.

<code>
#include <cstddef>
#include <new>

class FullQueue{};
class EmptyQueue{};




template<class ItemType>
class Queue
{
private:
int front; // front position
int rear; // rear position
int maxQue; // maximun number of
elements in the queue,
// including one
reserved element

ItemType* items; // it points to a
dynamically-allocated array
public:
Queue(int max); // parameterized class
constructor
Queue(); // default constructor;
queue created empty

Queue(const Queue<ItemType> &x); // copy
constructor;implicitly called
// for pass by value
void MakeEmpty(); // queue is made empty
bool IsEmpty(); // test if the queue is
empty
bool IsFull(); // test if the queue is
full
int length(); // return the number of
elements in the queue
void Print(); // print the value of
all elements in the
// queue from the front
to rear
void Enqueue(ItemType x); // insert x to the rear
of the queue
// Pre: the queue is
not empty
void Dequeue(ItemType &x); // delete the element
from the front of the queue
// Pre: the queue is
not empty
~Queue(); // destructor: memory
for dynamic array needs to be deallocated

};

template<class ItemType>
Queue<ItemType>::Queue()
{

items = new ItemType[maxQue];
front = maxQue;
rear = maxQue;

}

template<class ItemType>
Queue<ItemType>::Queue(int max)
{
maxQue = max + 1;
front = maxQue - 1;
rear = maxQue -1;
items = new ItemType[maxQue];

}

template<class ItemType>
Queue<ItemType>::Queue(const Queue<ItemType> &x)
{
front = x.front;
rear = x.rear;
int count = x.count;
for(int i=0;i<x.count;++i)
{
items = x.items;
}
}

template<class ItemType>
void Queue<ItemType>::MakeEmpty()
{

rear = maxQue - 1;
front = maxQue - 1;
}



template<class ItemType>
bool Queue<ItemType>::IsEmpty()
{

return (rear==front);
}

template<class ItemType>
bool Queue<ItemType>::IsFull()
{
return ((rear+1) % maxQue == front);
}

template<class ItemType>
int Queue<ItemType>::length()
{

return 0;
}

template<class ItemType>
void Queue<ItemType>::print()
{
int current;
current = rear;
do{
current = (current + 1) % maxQue;
std::cout << items[current] << std::endl;
}while(current != front);


}

template<class ItemType>
void Queue<ItemType>::Enqueue(ItemType x)
{
if(IsFull())
throw FullQueue();
else
{
rear = (rear+1)% maxQue;
items[rear]=x;

}
}

template<class ItemType>
void Queue<ItemType>::Dequeue(ItemType &x)
{
if(IsEmpty())
throw EmptyQueue();
else
{
front=(front +1)% maxQue;
x =items[front];

}
}

template<class ItemType>
Queue<ItemType>::~Queue()
{
delete[]items;
}

// main file
#include <cstdlib>
#include <cstddef>
#include <new>
#include <iostream>
#include "Queue.h"


using namespace std;

int main()
{

Queue<int> IntQueue;

int x;
try{

IntQueue.Dequeue(x);
}
catch(FullQueue exceptionObject)
{
cerr << "FullQueue exception thrown.(int) " << endl;
}
catch(EmptyQueue exceptionObject)
{
cerr << "EmptyQueue exception thrown.(int) " << endl;
}
IntQueue.Enqueue(1);
IntQueue.Enqueue(2);
IntQueue.Enqueue(3);
IntQueue.Enqueue(4);
cout << "int length 3 = " << "4" << endl;//IntQueue.length() <<
endl;
IntQueue.Dequeue(x);
cout << "int length 4 = " << "4" << endl;;//IntQueue.length() <<
endl;
IntQueue.Print();






Queue<float> FloatQueue;
float y;
try{

FloatQueue.Dequeue(y);
}
catch(FullQueue exceptionObject)
{
cerr << "FullQueue exception thrown.(float)" << endl;
}
catch(EmptyQueue exceptionObject)
{
cerr << "EmptyQueue exception thrown.(float)" << endl;

}
cout << endl;
FloatQueue.Enqueue(7.1);
cout << "float length 3 = " << FloatQueue.length() << endl;
FloatQueue.Enqueue(2.3);
cout << "float length 4 = " << FloatQueue.length() << endl;
FloatQueue.Enqueue(3.1);
FloatQueue.Dequeue(y);
FloatQueue.Print();






system("pause");
return 0;
</code>
 
H

Heinz Ozwirk

Sorry about that.

<code>
#include <cstddef>
#include <new>

class FullQueue{};
class EmptyQueue{};




template<class ItemType>
class Queue
{
private:
int front; // front position
int rear; // rear position
int maxQue; // maximun number of
elements in the queue,
// including one
reserved element

ItemType* items; // it points to a
dynamically-allocated array
public:
Queue(int max); // parameterized class
constructor
Queue(); // default constructor;
queue created empty

Queue(const Queue<ItemType> &x); // copy
constructor;implicitly called
// for pass by value
void MakeEmpty(); // queue is made empty
bool IsEmpty(); // test if the queue is
empty
bool IsFull(); // test if the queue is
full
int length(); // return the number of
elements in the queue
void Print(); // print the value of
all elements in the
// queue from the front
to rear
void Enqueue(ItemType x); // insert x to the rear
of the queue
// Pre: the queue is
not empty
void Dequeue(ItemType &x); // delete the element
from the front of the queue
// Pre: the queue is
not empty
~Queue(); // destructor: memory
for dynamic array needs to be deallocated

};

template<class ItemType>
Queue<ItemType>::Queue()
{

items = new ItemType[maxQue];
front = maxQue;
rear = maxQue;

}

template<class ItemType>
Queue<ItemType>::Queue(int max)
{
maxQue = max + 1;
front = maxQue - 1;
rear = maxQue -1;
items = new ItemType[maxQue];

}

template<class ItemType>
Queue<ItemType>::Queue(const Queue<ItemType> &x)
{
front = x.front;
rear = x.rear;
int count = x.count;
Click to expand...

'count' is not a member of Queue said:
for(int i=0;i<x.count;++i)
{
items = x.items;
Click to expand...


this->items is not valid. You hav to allocate some memory for your array of
pointers before you can assign pointers to it.
}
}
Click to expand...

Remember the "Rule of Three". If you need a user-defined copy c-tor, you
probably need a user-defined assignment operator, too.
template<class ItemType>
void Queue<ItemType>::MakeEmpty()
{

rear = maxQue - 1;
front = maxQue - 1;
}



template<class ItemType>
bool Queue<ItemType>::IsEmpty()
{

return (rear==front);
}

template<class ItemType>
bool Queue<ItemType>::IsFull()
{
return ((rear+1) % maxQue == front);
}

template<class ItemType>
int Queue<ItemType>::length()
{

return 0;
Click to expand...

If is rear greater than or equal to front, the length (number of elements in
queue) is rear - front. If it is less, the length is maxQue - front + rear
(or rear - front + maxQue). Also, if rear > front than rear - front ==
(rear - front + maxQue) % maxQue. So you the length of the queue is (rear -
front + maxQue) % maxQue.
}

template<class ItemType>
void Queue<ItemType>::print()
{
int current;
current = rear;
do{
current = (current + 1) % maxQue;
std::cout << items[current] << std::endl;
}while(current != front);
Click to expand...

This code doesn't work it the queue is empty. Use a for or pre-emptive while
loop instead. You should also display those data between front and rear, not
those undefined items between rear and front. What about

for (int current = front; current != rear; current = (current + 1) %
maxQue)
{
std::cout << ...;
}

But you have to apply the following changes, too, to use for this way...
}

template<class ItemType>
void Queue<ItemType>::Enqueue(ItemType x)
{
if(IsFull())
throw FullQueue();
else
{
rear = (rear+1)% maxQue;
items[rear]=x;
Click to expand...

In C++ (and C) it is more common to put something at the front position of a
container and make the rear position off by one, like it is with arrays,
where

int array[n];
array[0] = ...; /* legal */
array[n] = ...; /* error */

So using

items[rear] = x;
rear = (rear + 1) % maxQue;

is easier to understand for those accustomed to C++ or C.
}
}

template<class ItemType>
void Queue<ItemType>::Dequeue(ItemType &x)
{
if(IsEmpty())
throw EmptyQueue();
else
{
front=(front +1)% maxQue;
x =items[front];
Click to expand...

Again, swap assignment and increment:

x = items[front];
front = (front + 1) % maxQue;
}
}

template<class ItemType>
Queue<ItemType>::~Queue()
{
delete[]items;
}

// main file
#include <cstdlib>
#include <cstddef>
#include <new>
#include <iostream>
#include "Queue.h"


using namespace std;

int main()
{

Queue<int> IntQueue;

int x;
try{

IntQueue.Dequeue(x);
}
catch(FullQueue exceptionObject)
{
cerr << "FullQueue exception thrown.(int) " << endl;
}
catch(EmptyQueue exceptionObject)
{
cerr << "EmptyQueue exception thrown.(int) " << endl;
}
IntQueue.Enqueue(1);
IntQueue.Enqueue(2);
IntQueue.Enqueue(3);
IntQueue.Enqueue(4);
cout << "int length 3 = " << "4" << endl;//IntQueue.length() <<
endl;
IntQueue.Dequeue(x);
cout << "int length 4 = " << "4" << endl;;//IntQueue.length() <<
endl;
IntQueue.Print();






Queue<float> FloatQueue;
float y;
try{

FloatQueue.Dequeue(y);
}
catch(FullQueue exceptionObject)
{
cerr << "FullQueue exception thrown.(float)" << endl;
}
catch(EmptyQueue exceptionObject)
{
cerr << "EmptyQueue exception thrown.(float)" << endl;

}
cout << endl;
FloatQueue.Enqueue(7.1);
cout << "float length 3 = " << FloatQueue.length() << endl;
FloatQueue.Enqueue(2.3);
cout << "float length 4 = " << FloatQueue.length() << endl;
FloatQueue.Enqueue(3.1);
FloatQueue.Dequeue(y);
FloatQueue.Print();






system("pause");
return 0;
}

</code>
Click to expand...

HTH
Heinz
 
H

Howard

Sorry about that.
Click to expand...

Sorry about what? Please include what you're responding to.

template<class ItemType>
void Queue<ItemType>::print()
{
int current;
current = rear;
do{
current = (current + 1) % maxQue;
std::cout << items[current] << std::endl;
}while(current != front);


}
Click to expand...

That is the print function you're having problems with, right? So, what
happens? (Use your debugger and see!) If it's going into an infinite loop,
then that means that current never equals front, right? So, what's front
equal to?

Also, earlier you stated:
"Also I am unable to calculate the length of my queue. I started getting
compilation errors when I included a length function."
What does that mean? We can't tell what's wrong with code you don't show
us.

-Howard
 

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